Doc #38 — Fastener Production

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RECOMMENDED ACTIONS

NZ’s existing fastener stocks at distributors, retailers, and in workshop inventories are measured in thousands of tonnes and cover months to over a year of recovery-level consumption. No structure fails for want of a bolt in Month 1. The policy actions — classifying fasteners as controlled materials, issuing salvage guidance — are cheap directives that belong early. The inventory, machine shop survey, and production trials are institutional efforts that fold into the general stockpile audit and skills census over Months 2–6.

First month (Phase 1)

1. Classify fastener stocks as controlled materials. Prevent panic buying and hoarding of imported threaded fasteners, which are the category with the longest lead time to domestic substitution.
2. Confirm Pacific Steel (Otahuhu) nail and staple production is continuing (see Doc #105 for detailed actions on wire drawing and nail production).
3. Issue guidance to all construction and maintenance operations: Salvage and reuse all fasteners wherever possible. Straighten bent nails. Clean and reuse bolts. No fastener should be discarded unless damaged beyond recovery.

Months 2–3 (Phase 1)

4. Inventory fastener stocks at major NZ distributors and retailers. Contact Wurth, Hare & Forbes, Bolt & Nut NZ, Hobson Engineering, Mitre 10 distribution centres, Bunnings distribution centres, Placemakers, ITM, and all major industrial fastener suppliers. Capture total stocks by type (nails, screws, bolts, nuts, washers, rivets, staples) and by size. This folds into the national stockpile survey (Doc #1).
5. Allocate imported fastener stocks through a controlled distribution system. Threaded fasteners (screws, bolts, nuts) receive the highest rationing priority because they are the hardest to produce domestically. Nails and staples receive lower rationing priority because domestic production exists.
6. Begin bolt re-use and reconditioning programme. Collect used bolts from demolished structures and scrapped equipment. Sort by size, thread form, and condition. Clean, de-rust, re-lubricate, and redistribute usable bolts.
7. Standardise bolt sizes for recovery use. Identify 8–12 most-used bolt sizes (by diameter, length, and thread pitch) and prioritise all production and allocation around these standard sizes. Reducing the variety of sizes in circulation simplifies production and inventory management enormously.

Months 3–6 (Phase 1)

8. Survey NZ machine shops for thread-cutting capability. Determine the number and location of lathes with lead screws capable of single-point threading, stocks of taps and dies (by size and thread form), and the availability of thread-rolling equipment (if any exists domestically).²
9. Survey NZ engineering firms for bolt-making capability. Identify any NZ businesses that forge, head, or thread bolts or screws, even at small scale. Some specialist fastener firms may have limited production or finishing capability.

Months 6–12 (Phase 1–2)

10. Begin dedicated bolt production trials in NZ machine shops. Using existing lathes, forges, and die sets, produce sample batches of the most critical bolt sizes. Document production rates, material consumption, and quality. Establish realistic per-bolt production times for hand-threaded bolts (estimated 5–20 minutes per bolt depending on size, skill, and method).³
11. Design and begin fabrication of a bolt-heading machine suitable for production in NZ machine shops. Historical bolt-making machines from the 19th century provide design precedent – a mechanical upsetting press that forms a hexagonal head on a heated wire or rod blank.⁴
12. Assess thread-rolling feasibility. Thread rolling produces threads faster and stronger than cutting, but requires hardened thread-rolling dies. Determine whether NZ can produce functional thread-rolling dies from available tool steel, or whether the dies in existing stocks can be allocated to a centralised bolt-production facility.
13. Begin production of wood screws at Pacific Steel or supporting workshops. Wood screws require a gimlet point, a slotted or cross-recessed head, and a thread with a wider pitch than machine screws. Cam-operated wood screw-making machines were widespread in the 19th century and are within NZ’s capability to reproduce, though fabrication requires precision lathe and milling work (Doc #91).

First year (Phase 1–2)

14. Establish at least one dedicated bolt-production workshop in the Auckland region and one in the South Island (Christchurch or Dunedin). Equip each with heading machinery, threading capability (die heads or rolling dies), and heat treatment. Target output: hundreds to low thousands of bolts per day per facility.
15. Achieve domestic production of hex nuts. Nuts require punching or drilling a hole in a hex blank and tapping internal threads. Both operations are within NZ’s capability but benefit from dedicated tooling to achieve useful production rates.
16. Develop and distribute a NZ fastener standard specifying the standard sizes, thread forms, material grades, and markings for NZ-produced fasteners. Adopt metric coarse thread (ISO 261/262) as the national standard to avoid dual-standard confusion.⁵
17. Produce washers at scale. Flat washers are stamped discs with a centre hole – geometrically the least demanding fastener to produce, requiring only a press, punch, and die. Spring (Belleville) washers are more complex but achievable from spring steel strip (see Section 6.3).
18. Coordinate with Doc #105 (Fencing Wire, Nails, and Wire Drawing) for steel wire supply to nail, staple, and rivet production; and with Doc #92 (Blacksmithing) for hand-forged bolts and hardware in regions lacking machine-shop bolt production.

Years 2–3 (Phase 2)

19. Scale bolt and nut production toward thousands per day nationally. Refine production processes based on first-year experience.
20. Develop coach screws (lag screws) and large timber fasteners for heavy timber construction. These are large threaded fasteners that combine bolt-like strength with screw-like self-tapping capability in timber.
21. If thread-rolling proves feasible with NZ-produced dies, establish rolling as the primary threading method. Thread-rolled fasteners are stronger than cut-thread fasteners because rolling displaces rather than removes material, leaving the grain structure intact.⁶
22. Develop self-tapping screw production if demand warrants – self-tapping screws require a hardened point and case-hardened thread, which adds heat-treatment steps to the production process.
23. If maritime trade with Australia develops, prioritise import of thread-rolling dies, taps, and die sets in NZ-standard sizes. These are high-value, low-volume items that dramatically increase NZ bolt production capacity.

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ECONOMIC JUSTIFICATION

The cost of not producing fasteners

Like wire and nails (Doc #105), fasteners are not an optional product. Without them, timber construction stops, machinery cannot be assembled or repaired, fencing cannot be built, and infrastructure cannot be maintained. The question is not whether to produce fasteners but how to transition from imported supply to domestic production with the least disruption.

Labour requirements for Tier 1 (nails and staples)

Addressed in Doc #105. Pacific Steel’s existing nail-making operation requires an estimated 50–200 workers. No additional investment is needed beyond maintaining wire rod supply and consumables.

Labour requirements for Tier 2 (screws and bolts)

Machine-shop bolt production (initial method): A machinist producing bolts by forging, cutting to length, heading (by hand or simple press), and threading on a lathe can produce perhaps 20–60 bolts per day, depending on size and threading method.⁷ To produce 1,000 bolts per day – a fraction of NZ’s pre-event daily consumption but enough to cover critical repair and construction needs – requires approximately 20–50 dedicated machinists. This is a significant allocation of NZ’s most valuable tradespeople (Doc #145), but bolt production can be distributed across many workshops as a part-time activity alongside other machining work.

Dedicated bolt-making facility (target method): A purpose-built facility with heading press, thread-rolling or die-cutting equipment, and heat treatment can produce several thousand bolts per day with 10–30 workers. Establishing such a facility requires an estimated 3–10 person-years of engineering and fabrication effort for the machinery, plus 1–2 years of process development.⁸

Return on investment

The breakeven question is: at what point does domestic bolt production become more efficient than the alternative – which is cannibalising bolts from scrapped equipment and demolished structures? NZ has a large stock of bolts embedded in its built environment and machinery. In the short term (first 1–2 years), salvage and reuse is cheaper and faster than production. But salvage is a depleting resource – the most accessible bolts are recovered first, and each subsequent harvest is harder. By year 2–3, a functioning bolt-production facility pays for itself in reduced salvage effort and the ability to produce fasteners in sizes and quantities that salvage cannot reliably provide.

Estimate: The total investment to establish basic domestic bolt production capability is approximately 15–30 person-years of skilled labour over the first 2–3 years, distributed across machine shop work, forge construction, tooling fabrication, and process development. This investment sustains NZ’s ability to build and repair for decades.

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1. WHAT NZ CONSUMES AND WHERE IT COMES FROM

1.1 Fastener categories

NZ’s fastener consumption spans a wide range of products. The major categories, in rough order of volume:

Category	Typical materials	Primary uses	NZ domestic production?
Wire nails	Mild steel wire	Timber framing, cladding, pallets	Yes – Pacific Steel, Otahuhu
Fencing staples	Mild steel wire	Attaching fence wire to posts	Yes – Pacific Steel
Wood screws	Mild steel, zinc-plated	Timber joinery, furniture, fittings	No – all imported
Self-drilling screws	Hardened steel, zinc-plated	Roofing, cladding (COLORSTEEL)	No – all imported
Hex bolts and nuts	Medium-carbon steel, grade 4.6–8.8	Structural, machinery, automotive	No – all imported
Coach screws	Medium-carbon steel	Heavy timber connections	No – all imported
Machine screws	Mild to medium-carbon steel	Equipment assembly, electrical	No – all imported
Rivets (blind/pop)	Aluminium, steel	Sheet metal, light assembly	No – all imported
Solid rivets	Mild steel, copper	Traditional metalwork, boatbuilding	Producible from wire
Washers (flat and spring)	Mild steel, spring steel	Under bolt heads and nuts	No – all imported
Anchor bolts	Medium-carbon steel	Concrete connections	No – all imported

1.2 Scale of consumption

NZ’s total fastener imports are difficult to disaggregate precisely from trade data because fasteners are classified across multiple tariff headings. However, NZ imports an estimated several thousand tonnes of threaded fasteners (screws, bolts, nuts) per year, plus additional thousands of tonnes of nails, staples, and rivets.⁹ The total value of fastener imports is estimated in the hundreds of millions of NZD annually, reflecting the enormous volume and variety consumed by the construction, agricultural, and manufacturing sectors.

Assumption: Under recovery conditions, fastener consumption drops significantly – construction activity declines, manufacturing contracts, and reuse replaces new consumption for many applications. An estimate of 30–50% of pre-event consumption as the Phase 1–2 demand level is a starting assumption, but the actual figure depends on the pace of construction and repair activity.

1.3 Existing stocks

NZ holds substantial fastener inventories at the time of import cessation:

• Distributor and retailer stocks: Hardware retailers (Mitre 10, Bunnings, Placemakers, ITM), industrial suppliers (Wurth, Bolt & Nut, Hobson Engineering, Fastener Solutions), and specialist importers hold stocks measured in thousands of tonnes collectively. These are the primary buffer.
• Workshop inventories: Every engineering workshop, farm shed, construction site, and home garage holds fastener stocks. In aggregate, these represent a significant national inventory, though difficult to quantify.
• Embedded in the built environment: Billions of fasteners are currently installed in NZ buildings, vehicles, and machinery. These represent a long-term salvage resource. However, most embedded fasteners are not conveniently accessible – extraction requires demolition or disassembly, which is often more labour-intensive than new production.

Estimate: Total NZ fastener stocks at distribution and retail level – excluding embedded fasteners – might sustain 1–3 years of recovery-level consumption for nails (supplemented by domestic production) and 6–18 months for threaded fasteners (no domestic production until developed).¹⁰ This is a rough estimate and must be refined by the national census (Doc #8).

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2. TIER 1: NAILS, STAPLES, AND RIVETS

2.1 Nails and staples

Doc #105 (Fencing Wire, Nails, and Wire Drawing) covers nail and staple production in detail. The essential points for this document:

• Production chain exists domestically. NZ Steel Glenbrook (Doc #89) produces steel from domestic ironsand. Wire rod from Glenbrook feeds Pacific Steel at Otahuhu, which draws wire and produces nails and staples on existing heading machines.
• Wire rod supply is the critical dependency. Glenbrook does not currently produce wire rod – its rolling mill is configured for flat products. Adapting Glenbrook for rod production is a 6–18 month engineering project (Doc #89, Section 7). Until rod is available from Glenbrook, production depends on existing rod stockpiles.
• Nail-making machinery is mechanically straightforward and robust. Pacific Steel’s heading machines are mechanical devices with long service lives. The process – feed wire, cut to length, form head, form point – has been mechanically automated since the late 18th century.¹¹
• Hand-forged nails from blacksmiths (Doc #92) serve as a fallback and a supplement for small-scale or specialised production (e.g., boat nails, clinch nails, horseshoe nails). A skilled blacksmith produces 200–500 nails per day – insufficient for national supply but adequate for local needs.¹²

2.2 Rivets

Solid rivets are among the least demanding fasteners to produce. A rivet is a short piece of wire or rod with a pre-formed head on one end. The rivet is inserted through aligned holes in the parts to be joined, and the plain end is hammered (upset) to form a second head, clamping the parts together.

Production from wire: Solid rivets can be made on the same heading machines that produce nails, with minor tooling changes. The process is identical – cut wire to length, form head – except that the opposite end is left blunt rather than pointed. Pacific Steel could produce rivets as an extension of nail production with minimal adaptation.

Hand production: A blacksmith or any metalworker with a hammer, an anvil, and a rivet header (a plate with a hole sized to the rivet shank) can produce rivets from wire stock. Production rate is similar to hand nail-making – hundreds per day.

Blind (pop) rivets are a different matter. These are hollow aluminium or steel rivets with a mandrel, designed for one-sided installation. They require precision manufacturing and are not producible domestically in the near term. As blind rivet stocks deplete, NZ reverts to solid rivets, which require access to both sides of the joint – a constraint for some applications but one that was universal before the mid-20th century.¹³

2.3 Pins and cotter pins

Split cotter pins, clevis pins, dowel pins, and similar hardware are turned or drawn wire products within NZ’s existing machine shop capability. Cotter pins are made by bending a piece of wire in half – a task requiring no machinery at all. Clevis pins are short lengths of rod turned to diameter on a lathe with a drilled cross-hole for a cotter or split pin. These are low-complexity products for the machine shop network (Doc #91) – each requires only basic lathe and bench work – but their absence stops machinery and equipment from functioning.

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3. TIER 2: SCREWS AND BOLTS – THE THREADING CHALLENGE

3.1 Why threading is hard

A screw or bolt is a nail with a thread. The thread is what makes it fundamentally different – the helical groove allows the fastener to be driven into material (wood screws) or to clamp parts together with controllable tension (bolts). Producing that thread to the correct pitch, depth, and profile is the manufacturing challenge that separates Tier 1 from Tier 2.

Thread specifications are precise. An M12 bolt (12 mm nominal diameter) has a thread pitch of 1.75 mm for coarse thread, meaning each turn of the helix advances exactly 1.75 mm. The thread profile – a 60-degree V-form with specified root radius and crest – must be consistent along the entire threaded length. Bolts that do not thread smoothly into standard nuts are useless; bolts whose threads strip under load are dangerous.¹⁴

Three methods exist for producing threads:

Thread cutting (single-point): A lathe with a lead screw can cut threads by advancing a pointed cutting tool along a rotating workpiece at a controlled rate. This is the method used in NZ machine shops today for one-off and small-batch work. It is precise, versatile, and requires no specialised tooling beyond the lathe itself and a suitable cutting tool. But it is slow – threading a single bolt takes 3–10 minutes of machine time depending on bolt length and thread length, and a skilled machinist’s time is the scarcest resource in recovery NZ (Doc #145). Single-point threading is viable for critical bolts in non-standard sizes but cannot supply national demand.

Thread cutting (dies): A threading die is a circular tool with internal cutting edges that matches the desired thread form. The die is rotated around the bolt blank (or the blank is rotated through a stationary die), and the die cuts the external thread in a single pass. Dies are faster than single-point threading – perhaps 30–60 seconds per bolt for common sizes. Die sets for metric threads are widely held in NZ machine shops, home workshops, and hardware stores. The constraint is die wear: each die can thread a finite number of bolts (hundreds to thousands, depending on material and lubrication) before the cutting edges dull and the threads it produces degrade.¹⁵ Dies are imported and finite. Resharpening dies is possible but requires skill and diamond or cubic boron nitride lapping tools.

Thread rolling: The fastest and strongest method. Two hardened steel dies with the negative thread profile are pressed against opposite sides of a rotating blank. The dies cold-form the thread by displacing material rather than cutting it. Thread rolling is the standard industrial method for bolt production – modern bolt factories produce thousands of bolts per hour using multi-station forming machines.¹⁶ Thread-rolled bolts are stronger than cut-thread bolts because the metal grain follows the thread profile rather than being severed. The constraint: thread-rolling dies are precision-hardened tools, significantly more difficult to produce than cutting dies. NZ does not manufacture thread-rolling dies.

3.2 Thread forms: standardisation matters

NZ uses two thread standards:

• Metric (ISO): M-series threads per ISO 261/262. Coarse and fine pitch. The modern standard for all new equipment and construction. Most fasteners sold in NZ since the 1970s are metric.¹⁷
• Unified (Imperial/UNC/UNF): Older equipment, particularly agricultural machinery, vehicles manufactured before the 1980s, and some Australian and American equipment, uses Unified threads. A significant fraction of NZ’s installed equipment base still uses Unified threads.¹⁸

Recommendation for domestic production: Standardise on metric coarse thread (ISO 261) for all new NZ-produced fasteners. The metric coarse series covers all common sizes with a manageable number of dies. Producing both metric and Unified threads doubles the tooling requirement without increasing output. Legacy Unified bolts should be sourced from salvage and existing stocks; new production in Unified thread should be limited to specific critical applications where replacement is unavoidable.

3.3 Bolt production: the full process

Producing a hex bolt from wire rod requires the following steps:¹⁹

Step 1 – Wire rod or bar stock. Starting material is mild or medium-carbon steel rod from NZ Steel (Doc #89) or drawn wire from Pacific Steel (Doc #89). For Grade 4.6 bolts (the basic structural grade), mild steel with 0.15–0.30% carbon is adequate. For Grade 8.8 bolts (the standard high-strength grade used in structural and automotive applications), medium-carbon steel with 0.30–0.45% carbon is required, plus quenching and tempering heat treatment.²⁰

Step 2 – Cut to length. Shear or saw the rod to the required bolt length plus head-forming allowance.

Step 3 – Heading (forming the bolt head). The most equipment-dependent step. Options:

• Hot heading (forging): Heat the head end of the blank to orange-red (~900–1,000 degrees C) and upset it against a die to form the hex shape. A blacksmith (Doc #92) can do this with a hammer and a hex die (a plate with a hex hole), producing perhaps 30–100 bolts per day depending on size. A power hammer or mechanical press increases this to hundreds per day.²¹
• Cold heading: The blank is headed at room temperature in a mechanical press at high speed. Cold heading is the standard industrial method for bolt production – a cold heading machine can produce thousands of bolt blanks per hour. However, cold heading machines are specialised imported equipment. NZ may have some cold heading capability at fastener finishing firms, but this requires verification.²²
• Improvised heading: As a lowest-tooling fallback, a bolt head can be formed by forge-welding a separate hex piece onto a threaded rod, or by milling a hex shape from a larger-diameter bar. Both are slow and wasteful of material but functional for small quantities.

Step 4 – Threading. Apply the thread by one of the three methods described in Section 3.1.

Step 5 – Heat treatment (for Grade 8.8 and above). Higher-strength bolts require quenching (heating to ~830–860 degrees C and rapid cooling in oil or water) followed by tempering (reheating to ~425–500 degrees C and air cooling). This produces the martensite-to-tempered-martensite transformation that gives Grade 8.8 bolts their characteristic balance of strength and toughness.²³ Heat treatment requires a furnace capable of reaching ~900 degrees C with reasonable temperature uniformity, and a quench tank. Both are achievable in NZ machine shops and blacksmith forges (Doc #91, Doc #92). Temperature control is the critical variable – over-tempering produces a weak bolt; under-tempering produces a brittle one. Without precise pyrometry, hardness testing (a Rockwell or Brinell tester) after heat treatment is the quality check.

Step 6 – Surface treatment (optional). Imported bolts are typically zinc-plated or hot-dip galvanised for corrosion protection. NZ cannot produce zinc (Doc #89). NZ-produced bolts will be uncoated (“black”) unless oiled or painted. In outdoor applications, uncoated mild steel bolts corrode significantly faster than zinc-plated equivalents – expected service life in exposed conditions drops from decades to perhaps 3–10 years depending on environment.²⁴ Protective measures include oiling, painting, or replacing more frequently, but none approaches the durability of hot-dip galvanising.

3.4 Nut production

A nut is a block of steel with a hex exterior and an internally threaded hole. Production requires:

1. Blank production: Cut hex bar stock to thickness, or punch/forge hex blanks from flat bar or plate. Hex bar stock is imported; under recovery conditions, hexagonal blanks would be forged or milled from round or square bar.
2. Drilling: Drill the through-hole to the thread minor diameter.
3. Tapping: Cut the internal thread using a tap – a hardened tool with the male thread profile and fluted cutting edges. Tapping is faster than external die-threading for equivalent sizes because nuts are shorter than bolts. A single tap can produce hundreds to thousands of nuts before dulling, depending on material and lubrication.²⁵
4. Chamfering: Remove the sharp edges on both faces of the nut to allow easy bolt engagement.

Nut production rates: With a drill press and tap, a worker can produce perhaps 40–100 nuts per hour for common sizes. With a dedicated multi-spindle tapping machine (if available), rates increase to several hundred per hour.

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4. WOOD SCREWS

4.1 Why wood screws are different

Wood screws differ from machine screws (bolts) in several ways that affect production:

• Thread form: Wood screw threads have a wider pitch (fewer threads per unit length) and a sharper profile than machine threads, designed to cut into and grip timber fibres rather than mate with a pre-threaded nut.²⁶
• Gimlet point: The pointed tip of a wood screw is designed to self-pilot into timber without a pre-drilled hole (though pilot drilling is standard practice for hardwoods and large screws).
• Head form: Countersunk (flat) heads, raised countersunk, pan, and round head forms. Countersunk heads require a conical underside formed during heading.
• Drive recess: Slotted, Phillips cross, and Pozidriv are the common drive types. Producing a slotted head requires milling a slot across the formed head – a single milling pass. Phillips and Pozidriv recesses require a punch die matching the recess profile – more complex but producible.

4.2 NZ wood screw production

Wood screws were manufactured on dedicated screw machines from the early 19th century. The basic process – head forming (cold or hot), thread cutting (using a chaser or die), and point forming – is well documented in historical engineering literature.²⁷ The machinery, while more complex than nail-making equipment, is within NZ’s capability to build or adapt.

Intermediate solution: NZ can produce functional wood screws on existing lathes by turning down the shank, cutting the thread with a die, forming the point, and slotting the head. This is impractically slow for mass production but adequate for critical small-batch needs – e.g., marine hardware, hinge screws, or structural timber connections where nails are inadequate.

Production solution: A wood screw machine – a cam-operated lathe that automatically feeds wire, forms the head, cuts the thread, forms the point, and parts off the finished screw – can be designed and built by NZ machine shops. 19th-century screw machines were manufactured by firms such as the American Screw Company and Harvey & Company and are well documented in patent literature and engineering archives.²⁸ NZ’s machine shop capability (Doc #91) is sufficient to reproduce these designs, given availability of tool steel for cams and chasers, cast iron or steel for the machine frame (Doc #94), and 2–6 months of machinist time for design, fabrication, and debugging per machine.

4.3 When are screws essential?

Not every application that currently uses screws actually requires them. In many cases, nails or bolts can substitute:

• Timber framing: Nails are the traditional and standard fastener. Screws are used in NZ framing primarily in earthquake-prone areas where building code requires specific connection hardware (hold-down bolts, strap ties). Where screws are code-specified, bolts can often substitute.
• Cladding and roofing: Self-drilling screws are the modern standard for fixing COLORSTEEL roofing and cladding to steel purlins. In recovery construction, timber purlins with nails or clout nails can replace steel purlins with screws for many applications, though nailed roofing iron has lower pull-through resistance in high winds and requires more frequent inspection and re-nailing than screwed connections.
• Furniture and joinery: Screws provide a removable, adjustable connection. Traditional joinery (mortise and tenon, dovetail, dowel) provides permanent connections without any metal fasteners, but requires significantly higher skill, more time per joint, and does not permit easy disassembly for repair or reconfiguration.
• Machinery and equipment assembly: This is where screws and bolts are genuinely irreplaceable. Threaded fasteners provide controlled clamping force and can be disassembled for maintenance – no substitute exists for bolted machinery connections.

Conclusion: In Phase 1–2, screw demand can be significantly reduced by reverting to nails and traditional joinery for construction, and reserving screws and bolts for machinery, structural connections, and applications where clamping force or removability is essential. This reduces the pressure on the Tier 2 production chain during its development period.

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5. SELF-DRILLING AND SELF-TAPPING SCREWS

5.1 What they are

Self-drilling screws (commonly called “tek screws”) have a drill-point tip that drills its own pilot hole as the screw is driven, followed by a self-tapping thread that forms its own mating thread in the drilled hole. They are the dominant fastener for NZ’s COLORSTEEL roofing and cladding industry – virtually every steel-clad roof installed in NZ since the 1980s is held on with self-drilling screws.²⁹

5.2 Why they are difficult to produce

Self-drilling screws require:

• Case hardening: The drill point and first few thread turns must be hardened to cut through steel sheet, while the screw body must remain tough to resist shearing. This requires controlled case hardening (carburising or carbonitriding) – a heat treatment process that hardens the surface while leaving the core ductile.³⁰
• Precise point geometry: The drill point must be ground to a specific included angle and lip relief to drill cleanly without walking or binding.
• Neoprene washer (for roofing): Roofing tek screws incorporate a bonded neoprene or EPDM rubber washer under the hex head to seal the hole against water penetration. NZ does not produce these sealing washers.

5.3 Practical assessment

Self-drilling screw production is at the difficult end of NZ’s fastener capability. Case hardening is achievable in NZ (charcoal pack carburising was a standard blacksmithing technique before industrialisation),³¹ but achieving consistent case depth and hardness across thousands of screws requires furnace temperature control and process development that takes months to years to calibrate.

Realistic pathway: NZ should not attempt self-drilling screw production in the near term. Instead:

• Ration existing stocks for repair of existing COLORSTEEL roofing.
• For new construction, design with timber purlins and nailed roofing iron (the pre-tek-screw method that served NZ for over a century).
• Where steel-to-steel connections are unavoidable, use bolts through pre-drilled holes.

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6. WASHERS

6.1 Why washers matter

Washers distribute bolt clamping force over a larger area of the joined material, preventing the bolt head or nut from embedding into soft surfaces (timber, thin sheet, soft metal). They also reduce friction during tightening, allowing more consistent preload. A bolt without a washer in timber gradually sinks into the wood as the timber shrinks and creeps, losing clamping force.³²

6.2 Flat washer production

Flat washers are among the least demanding fastener products to manufacture. They are stamped from sheet steel using a punch and die set:

1. Position sheet steel (1–3 mm thickness) in a press.
2. Punch the centre hole.
3. Punch the outer diameter.
4. The washer drops out of the die.

A fly press (a screw-operated mechanical press, common in NZ engineering workshops) with hardened punch and die tooling can produce flat washers at rates of several hundred per hour. The tooling itself – a cylindrical punch and a matching die cavity – can be made by any competent machinist (Doc #91) from tool steel or hardened mild steel.³³

Material: Sheet steel from NZ Steel Glenbrook (Doc #89). Even offcuts and scrap sheet from other fabrication work serve as washer stock.

6.3 Spring washers

Spring (split) washers and Belleville (disc) washers provide a locking function that resists bolt loosening under vibration. Production requires spring-grade steel strip, formed and heat-treated. Spring steel supply depends on NZ Steel’s ability to produce medium- to high-carbon steel strip (Doc #89); the specific alloy and temper requirements for spring washers are well-established in engineering references but the NZ supply chain is unverified. Spring washer production is achievable once spring steel strip is available but is a Phase 2–3 capability.

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7. FASTENER QUALITY AND TESTING

7.1 Why quality matters for threaded fasteners

A nail that is slightly off-diameter or has an imperfect head still works. A bolt with an incorrect thread pitch, insufficient strength, or brittle heat treatment can fail catastrophically under load – potentially causing structural collapse, equipment failure, or injury. Threaded fasteners are stressed components whose failure can be dangerous.

This means NZ-produced bolts must be tested before being used in structural or safety-critical applications. The standard tests:³⁴

Thread gauge testing: Go/no-go gauges check that the thread profile is correct – the bolt screws smoothly into a standard nut (go), and does not screw into an undersized nut (no-go). Thread gauges are precision tools – NZ must preserve its existing stock of thread gauges and allocate them to bolt production facilities. Thread gauge production from scratch is a precision machining challenge addressed in Doc #91.

Tensile testing: A bolt is loaded in tension to failure. The failure load must exceed the minimum specified for its grade (e.g., Grade 8.8 bolts must withstand 800 MPa tensile stress and 640 MPa proof stress). Tensile testing requires a tensile testing machine – NZ has these at universities (University of Auckland, University of Canterbury, Massey, AUT), HERA (Heavy Engineering Research Association), and some commercial testing laboratories.³⁵

Hardness testing: A quick, non-destructive check that correlates with strength. Rockwell, Brinell, or Vickers hardness testing is available at most NZ engineering workshops and educational institutions. Grade 8.8 bolts should test approximately 22–32 HRC (Rockwell C hardness) after quenching and tempering.³⁶

Proof loading: The entire bolt is loaded to its proof load (the load it must sustain without permanent deformation) and released. If the bolt does not permanently stretch, it passes.

7.2 Grade marking

NZ-produced bolts should be marked with their strength grade (e.g., “4.6” or “8.8” on the bolt head) and a producer mark. This is standard ISO practice and allows users to identify bolt capability. Marking can be achieved by stamping the head during or after heading – a letter or number punch struck into the hot or cold head.³⁷

Critical safety point: An unmarked bolt of unknown grade must be treated as the lowest grade (4.6) for design purposes. Using an unmarked bolt in an application designed for Grade 8.8 risks failure. This is why marking is not cosmetic – it is a safety function.

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8. SUBSTITUTES AND ALTERNATIVES TO METAL FASTENERS

8.1 Wooden fasteners

Timber construction does not inherently require metal fasteners. Traditional timber framing used:

• Treenails (trunnels): Wooden dowels driven through drilled holes to pin mortise-and-tenon joints. Made from hardwood (in NZ, native hardwoods such as rata, puriri, or matai; or seasoned eucalyptus). A treenail in a properly fitted joint is strong in shear and does not corrode.³⁸
• Wedged mortise and tenon: Joints held by the geometry of the cut timber plus wooden wedges. No metal required.
• Dowels: Short wooden cylinders glued or driven into drilled holes to align and reinforce butt joints.

These methods are slower and require higher skill than nailing or screwing, but they use only timber – a material NZ has in abundance. For heavy structural work (post-and-beam buildings, bridge framing, wharf construction), traditional joinery is a viable and time-proven alternative to metal fasteners.

8.2 Lashing and binding

For temporary structures, scaffolding, and some agricultural applications, wire binding (from NZ-drawn wire, Doc #105), harakeke fibre lashing (Doc #100), or rope lashing can substitute for metal fasteners. These are not structural equivalents – lashed joints are weaker and less durable than bolted joints – but they serve where permanence is not required.

8.3 Traditional NZ lashing, jointing, and non-metal fastening

Traditional NZ construction used lashing, jointing, and non-metal fastening systems that sustained all building in Aotearoa for centuries before European contact. These techniques become directly relevant when metal fastener stocks are depleted or rationed, and provide tested alternatives for timber construction, structural lashing, and marine applications.

Lashing with muka and harakeke cord: Muka (the fine fibre extracted from harakeke leaf by kairaranga using traditional techniques) produces cord of exceptional tensile strength relative to its weight.³⁹ Properly prepared muka cord was the structural lashing material for waka, whare, and other major constructions. Harakeke cord lashing is not a crude expedient – Māori constructions lashed with muka were engineered to last for decades and to flex under load rather than fracture, a characteristic that metal-fastened rigid frames do not share. Raw harakeke strip (before muka extraction) also serves as a robust lashing material for less demanding applications. Doc #100 covers harakeke fibre production, including cultivar selection, sustainable harvest, and fibre processing.

Waka construction jointing: Traditional waka (canoe) construction required joining large timber components – hull strakes, thwarts, outrigger booms – under conditions of high stress, saltwater exposure, and dynamic loading. The jointing methods employed are structurally demanding by any measure:

• Lashing through drilled holes: Strakes were joined at the gunwale by lashing muka cord through regularly spaced drilled or adze-cut holes along the plank edges, with the cord pulled tight under tension to clamp the joint. This technique creates a flexible but strong seam that tolerates the working of a hull in seaway conditions better than a rigid fastened joint.
• Carved housing joints: Major structural members (outrigger booms to hull, cross-beams to hulls on waka hourua) were fitted with carved housing joints – shaped recesses and projections that resist shear and racking loads – before being lashed. The geometry carries the structural load; the lashing maintains clamping pressure.
• Wooden pegs and dowels: Hardwood pegs (treenails) were used alongside lashing in waka planking to align strakes and prevent differential movement while the lashing was applied and set.

These techniques are directly transferable to timber boat-building (Doc #138, Doc #141) and to any heavy timber construction where metal bolts are unavailable.

Whare construction fastening: Traditional whare (dwellings) and wharenui (meeting houses) used a comprehensive non-metal fastening system:

• Pou (post) and rafter jointing: The framework of a whare was joined by a combination of carved housing joints (notched recesses in the pou that seat the rafters and plates), lashing at critical joints, and the weight and geometry of the structure itself distributing loads. No metal fasteners were required for structural integrity.
• Tukutuku panel attachment: Interior wall panels (tukutuku) are woven harakeke, kiekie, or pingao strands worked between vertical rods lashed to the wall framing. The lashing and weaving is itself a fastening system, integrating cladding with structure.
• Raupō and raupo roof binding: Traditional roof thatching used harakeke cord lashing to bind bundles of raupō or similar material to roof purlins. This is directly applicable to emergency roofing on recovery-era structures where roofing iron and self-drilling screws are unavailable.

Practical assessment for recovery: Mātauranga Māori fastening techniques sustained all construction in NZ for centuries before European contact and remain functional approaches for:

• Temporary and semi-permanent structures where metal fastener rationing makes other methods preferable
• Waka and small boat construction (the flexibility of lashed joints is advantageous in marine use)
• Emergency roofing and shelter where speed and available materials matter more than longevity
• Agricultural structures (yards, shelters, light fencing reinforcement) in regions where fastener supply has lapsed

The honest limitation is labour intensity: lashing a joint requires more time than driving a nail or threading a bolt. The tradeoff is favourable when the alternative is waiting for rationed metal fasteners rather than building with available materials. These techniques require hands-on learning from experienced practitioners – published sources alone are not adequate for skill acquisition.

Reference: Doc #160 (Heritage Skills Preservation) covers traditional Māori technology systems. Doc #100 covers harakeke fibre production. Doc #138 and Doc #141 cover waka and timber boatbuilding applications.

8.4 Adhesives

Hide glue, casein glue (from milk protein), and pine pitch are NZ-producible adhesives that serve some fastening functions in furniture, joinery, and light construction (Doc #47). They do not substitute for metal fasteners in structural or load-bearing applications.

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CRITICAL UNCERTAINTIES

Uncertainty	Impact if wrong	Resolution method
Total NZ threaded fastener inventory (distribution, retail, workshop stocks)	If smaller than estimated, the gap before domestic production comes online is larger and more disruptive. If larger, more time for development.	National census (Doc #8) with fasteners as a specific category.
NZ machine shop thread-cutting capacity (number of lathes with lead screws, tap and die stocks)	If less than assumed, bolt production ramp-up is slower.	Survey of machine shops – first month (Doc #38).
Existence of any cold heading or thread-rolling equipment in NZ	If some exists, bolt production capacity is immediately higher than assumed. If none, all production must start from forging and die-cutting.	Census of NZ engineering and fastener firms.
Glenbrook’s ability to produce medium-carbon wire rod for Grade 8.8 bolts	If achievable, high-strength bolts can be produced domestically. If not, all NZ-produced bolts are limited to Grade 4.6 until trade develops.	Metallurgical assessment at Glenbrook (Doc #89).
Tap and die stock durability under intensive production use	If dies wear faster than expected, die resharpening or replacement becomes a critical bottleneck.	Empirical testing during initial bolt production trials.
Tool steel availability for thread-rolling die fabrication	If sufficient tool steel exists in NZ workshops and distributor stocks, thread rolling may be achievable in Phase 2. If not, die-cutting remains the primary method.	National inventory of tool steel (Doc #8, Doc #38).
Screw demand under modified construction methods	If construction adapts effectively to nail-based methods, screw demand drops significantly. If adaptation is slow or incomplete, screw shortage becomes acute.	Construction sector consultation and building code adaptation – first 3 months.
Self-drilling screw stocks and depletion rate	Determines how long COLORSTEEL roof maintenance can continue with existing methods.	Distributor and retailer inventory (Doc #8).

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CROSS-REFERENCES

• Doc #1 – National Emergency Stockpile Strategy (fastener stocks as requisitioned category)
• Doc #8 – National Skills and Asset Census (fastener inventory, machine shop survey, threading equipment census)
• Doc #17 – Engineering Reference Tables (bolt specifications, thread data, torque tables)
• Doc #33 – Tires (vehicle assembly – fasteners required for wheel nuts, suspension bolts)
• Doc #52 – Wire Rope Production (rivet and pin connections in rope terminations)
• Doc #74 – Pastoral Farming (fencing hardware – staples, wire strainers requiring bolts)
• Doc #89 – NZ Steel Glenbrook (steel supply for all fastener production; wire rod development)
• Doc #91 – Machine Shop Operations (thread cutting, die-making, bolt production, lathe capability)
• Doc #92 – Blacksmithing (hand-forged bolts, nails, hardware, heading capability)
• Doc #94 – Foundry and Casting (die blanks, heading tool castings)
• Doc #94 – Welding Consumables (wire supply for welded connections as bolt alternative)
• Doc #97 – Cement and Concrete (anchor bolts, embedded fasteners for concrete construction)
• Doc #100 – Harakeke Fibre (lashing as fastener substitute; muka cord production)
• Doc #105 – Fencing Wire, Nails, and Wire Drawing (nail and staple production; wire rod supply; the primary companion document)
• Doc #138 – Sailing Vessel Design (marine fasteners; copper and bronze bolts for hull fastenings)
• Doc #157 – Trade Training Priorities (machinist and fastener-production training)
• Doc #160 – Heritage Skills Preservation (traditional lashing, jointing, and non-metal fastening techniques)

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1. NZ threaded fastener manufacturing: NZ has no significant domestic screw or bolt manufacturing. Some NZ engineering firms finish or assemble fastener products (e.g., cutting to length, applying coatings, assembling sets), but the core manufacturing – heading and threading of screws and bolts – is performed overseas, primarily in China, Taiwan, Japan, and Australia. See: NZ fastener industry sources; Fasteners & Fixing Association (NZ).↩︎

2. Thread-cutting capability in NZ machine shops: Most NZ machine shops with engine lathes have lead screws and change gears or quick-change gearboxes that enable single-point threading. Additionally, tap and die sets in metric and Unified thread forms are widely held. The total number of lathes with threading capability in NZ is unknown but is likely in the hundreds to low thousands. See Doc #8 for the broader machine shop census framework.↩︎

3. Bolt production time by hand methods: Producing a single bolt by forging a head, cutting to length, and threading with a die takes approximately 5–20 minutes depending on bolt size, worker skill, available tooling, and whether the heading is done hot (forge) or on a press. This estimate is based on general metalworking experience and historical accounts of pre-industrial bolt making. With practice and dedicated tooling, the lower end of this range is achievable for common sizes.↩︎

4. Bolt-making machinery history: Dedicated bolt-making machines were developed in the early 19th century. Micah Rugg of Connecticut patented a bolt-heading machine in 1818; William Keane of England developed bolt-making machinery around 1830. By mid-century, bolt factories using mechanical headers and thread-cutting die heads were widespread. These machines are well documented in historical engineering literature and patent archives. See: Roe, J.W., “English and American Tool Builders,” Yale University Press, 1916.↩︎

5. ISO metric thread standard: ISO 261 (general purpose metric screw threads) and ISO 262 (selected sizes for general use) define the metric coarse and fine thread series used worldwide and adopted by NZ through joint Australian/NZ standards (AS/NZS). NZ transitioned from Imperial (BSW, BSF) to metric threads beginning in the 1970s, with Unified (UNC/UNF) used as a transitional and American-origin standard. See: Standards NZ; ISO 261:1998.↩︎

6. Thread rolling vs. thread cutting: Thread rolling produces a stronger thread than cutting because the material grain flows continuously around the thread profile rather than being cut through. Rolled threads exhibit approximately 10–30% higher fatigue strength compared to cut threads of the same grade. Thread rolling also produces threads faster and wastes no material (unlike cutting, which removes material as chips). See: “Thread Rolling,” ASM Handbook, Volume 14A: Metalworking: Bulk Forming.↩︎

7. Bolt production time by hand methods: Producing a single bolt by forging a head, cutting to length, and threading with a die takes approximately 5–20 minutes depending on bolt size, worker skill, available tooling, and whether the heading is done hot (forge) or on a press. This estimate is based on general metalworking experience and historical accounts of pre-industrial bolt making. With practice and dedicated tooling, the lower end of this range is achievable for common sizes.↩︎

8. Bolt-making machinery history: Dedicated bolt-making machines were developed in the early 19th century. Micah Rugg of Connecticut patented a bolt-heading machine in 1818; William Keane of England developed bolt-making machinery around 1830. By mid-century, bolt factories using mechanical headers and thread-cutting die heads were widespread. These machines are well documented in historical engineering literature and patent archives. See: Roe, J.W., “English and American Tool Builders,” Yale University Press, 1916.↩︎

9. NZ fastener imports: NZ imports the vast majority of its threaded fastener consumption. Statistics NZ trade data shows imports of screws, bolts, nuts, and washers classified under HS tariff headings 7317 (nails, staples), 7318 (screws, bolts, nuts, washers), and related headings. Total import value across all fastener categories is estimated in the hundreds of millions of NZD annually. See: Statistics NZ, “Overseas Merchandise Trade.” https://www.stats.govt.nz/↩︎

10. NZ fastener stock depletion timeline: This is a rough estimate. NZ distributor and retailer fastener stocks represent perhaps 3–6 months of normal consumption. Under reduced recovery consumption (estimated 30–50% of normal), stocks might last 6–18 months for most categories. Nails deplete slower because domestic production supplements stocks. Self-drilling screws may deplete faster because they are consumed in large quantities for roofing repair (a high-priority activity) and have no domestic substitute. These estimates require validation through the national census.↩︎

11. History of nail and screw making: Wire nails were first manufactured by machine in the late 18th century, progressively replacing hand-forged (blacksmith) nails and cut nails (stamped from sheet). Wood screw machines were developed in the early 19th century, with key inventions by Thomas J. Sloan (pointed screw, 1836) and others. See: Nelson, L.H., “Nail Chronology as an Aid to Dating Old Buildings,” AASLH Technical Leaflet 48, 1968; Rybczynski, W., “One Good Turn: A Natural History of the Screwdriver and the Screw.”↩︎

12. Blacksmith nail production rates: Historical estimates of blacksmith nail production vary. A skilled nailer (specialist nail-making smith) in the pre-industrial era could produce 1,000–2,000 nails per day for small nails, or 200–500 per day for larger nails. A general blacksmith producing nails as one of many tasks would produce fewer. See: Landes, D.S., “The Unbound Prometheus”; historical accounts of colonial New Zealand ironworking.↩︎

13. Blind (pop) rivet history: The blind rivet was invented by the British aircraft manufacturer George Tucker in the 1930s for aircraft construction where only one side of the joint was accessible. Before blind rivets, all riveted joints required access to both sides – one person holding a bucking bar on the shop head side while another drove the rivet from the other side. See: general fastener engineering references; aviation history.↩︎

14. Thread specification precision: ISO metric thread specifications define thread pitch, major diameter, minor diameter, pitch diameter, crest and root forms, and tolerances. For example, an M12 x 1.75 bolt has a major diameter of 12.000 mm, pitch diameter of 10.863 mm, and minor diameter of 10.106 mm, with tolerance class 6g providing a tolerance band of approximately 0.05–0.15 mm depending on the dimension. See: ISO 261; ISO 965-1 (tolerances).↩︎

15. Tap and die life: The number of parts a tap or die can produce before requiring resharpening depends on the workpiece material, cutting speed, lubrication, and the tap/die material and coating. For cutting steel with HSS taps, typical life is 200–2,000 holes before resharpening is needed. For dies, life is somewhat longer because the die geometry is more robust. Hard-coated (TiN, TiAlN) taps last 2–5x longer than uncoated HSS. See: standard machining reference data; Machinery’s Handbook.↩︎

16. Thread rolling process: Thread rolling is a cold-forming process in which hardened dies with the thread profile in negative impression are pressed against a rotating blank, plastically deforming the surface to form the thread. Two main types exist: flat-die rolling (the blank rolls between two flat die plates) and cylindrical-die rolling (the blank rolls between two or three rotating cylindrical dies). Production rates of 30–300+ bolts per minute are typical for automated thread-rolling machines. See: “Thread Rolling,” ASM Handbook, Volume 14A.↩︎

17. ISO metric thread standard: ISO 261 (general purpose metric screw threads) and ISO 262 (selected sizes for general use) define the metric coarse and fine thread series used worldwide and adopted by NZ through joint Australian/NZ standards (AS/NZS). NZ transitioned from Imperial (BSW, BSF) to metric threads beginning in the 1970s, with Unified (UNC/UNF) used as a transitional and American-origin standard. See: Standards NZ; ISO 261:1998.↩︎

18. Imperial and Unified threads in NZ: NZ’s legacy equipment base includes significant quantities of BSW (British Standard Whitworth), BSF (British Standard Fine), UNC (Unified National Coarse), and UNF (Unified National Fine) threaded fasteners. Agricultural machinery, vintage vehicles, industrial plant installed before the 1980s, and some military equipment use these thread forms. Maintaining a repair capability for these threads requires retaining appropriate tap and die sets, which are no longer manufactured domestically. See: NZ engineering standards history; Standards NZ.↩︎

19. Thread rolling process: Thread rolling is a cold-forming process in which hardened dies with the thread profile in negative impression are pressed against a rotating blank, plastically deforming the surface to form the thread. Two main types exist: flat-die rolling (the blank rolls between two flat die plates) and cylindrical-die rolling (the blank rolls between two or three rotating cylindrical dies). Production rates of 30–300+ bolts per minute are typical for automated thread-rolling machines. See: “Thread Rolling,” ASM Handbook, Volume 14A.↩︎

20. Bolt grades and heat treatment: ISO 898-1 specifies mechanical properties for carbon steel and alloy steel bolts. Grade 4.6: tensile strength 400 MPa, yield 240 MPa, no heat treatment required (hot-rolled or cold-drawn low-carbon steel). Grade 8.8: tensile strength 800 MPa, yield 640 MPa, requires quenching and tempering of medium-carbon steel (0.15–0.40% carbon with boron, or 0.25–0.55% carbon without). Heat treatment parameters: austenitise at 830–860 degrees C, quench in oil or water, temper at 425–500 degrees C. Resulting hardness approximately 22–32 HRC. See: ISO 898-1; standard heat-treatment references.↩︎

21. Power hammer bolt heading rates: A blacksmith with a power hammer (typically 25–75 kg hammer weight) can head bolt blanks significantly faster than hand forging, with the heading operation itself taking 10–30 seconds per bolt for common sizes (M10–M20). The overall bolt production rate including heating, positioning, heading, and trimming is estimated at 100–400 per day per forge station, depending on bolt size, operator skill, and whether the blanks are pre-cut. This is a practitioner estimate based on general forging experience; no specific NZ production data exists.↩︎

22. Cold heading of bolts: Cold heading (also called cold forging) is the standard industrial method for forming bolt heads from wire stock at room temperature using high-speed mechanical presses. The process achieves very high production rates (30–300 bolts per minute) and produces a strong grain-flow pattern in the head. Cold heading machines are specialised, precision equipment manufactured by firms such as National Machinery (USA), Sacma (Italy), and Chun Zu (Taiwan). NZ is unlikely to have any cold heading machines dedicated to bolt production, though some may exist in other metalforming applications. See: “Cold Heading,” ASM Handbook, Volume 14A.↩︎

23. Bolt grades and heat treatment: ISO 898-1 specifies mechanical properties for carbon steel and alloy steel bolts. Grade 4.6: tensile strength 400 MPa, yield 240 MPa, no heat treatment required (hot-rolled or cold-drawn low-carbon steel). Grade 8.8: tensile strength 800 MPa, yield 640 MPa, requires quenching and tempering of medium-carbon steel (0.15–0.40% carbon with boron, or 0.25–0.55% carbon without). Heat treatment parameters: austenitise at 830–860 degrees C, quench in oil or water, temper at 425–500 degrees C. Resulting hardness approximately 22–32 HRC. See: ISO 898-1; standard heat-treatment references.↩︎

24. Corrosion of uncoated vs. galvanised steel fasteners: Hot-dip galvanised bolts (per AS/NZS 1214) in outdoor exposure typically provide 20–50+ years of service depending on environment category (ISO 9223). Uncoated mild steel in the same environments corrodes at approximately 10–80 micrometres per year, with coastal and industrial environments at the high end. For a standard M12 bolt with ~1.5 mm of sacrificial cross-section, this translates to roughly 3–10+ years before significant strength loss in sheltered-to-moderate exposure, and less in severe coastal or geothermal environments. See: AS/NZS 2312 (Guide to the Protection of Structural Steelwork); ISO 9223 (Corrosion of Metals — Corrosivity of Atmospheres).↩︎

25. Tap and die life: The number of parts a tap or die can produce before requiring resharpening depends on the workpiece material, cutting speed, lubrication, and the tap/die material and coating. For cutting steel with HSS taps, typical life is 200–2,000 holes before resharpening is needed. For dies, life is somewhat longer because the die geometry is more robust. Hard-coated (TiN, TiAlN) taps last 2–5x longer than uncoated HSS. See: standard machining reference data; Machinery’s Handbook.↩︎

26. Wood screw thread form: Wood screw threads are designed to cut into timber and grip by wedging the fibres apart. The thread form has a wider pitch (fewer threads per inch for equivalent diameter), a sharper crest angle (typically 60 degrees but with a narrower flat crest), and a deeper thread depth relative to the minor diameter compared to machine threads. The gimlet point is typically a cone angle of 40–60 degrees. See: standard fastener engineering references.↩︎

27. History of nail and screw making: Wire nails were first manufactured by machine in the late 18th century, progressively replacing hand-forged (blacksmith) nails and cut nails (stamped from sheet). Wood screw machines were developed in the early 19th century, with key inventions by Thomas J. Sloan (pointed screw, 1836) and others. See: Nelson, L.H., “Nail Chronology as an Aid to Dating Old Buildings,” AASLH Technical Leaflet 48, 1968; Rybczynski, W., “One Good Turn: A Natural History of the Screwdriver and the Screw.”↩︎

28. Historical wood screw machines: Wood screw-making machines were developed in the late 18th and early 19th centuries, with key developments by David Wilkinson (1798), Thomas J. Sloan (1836, pointed screw), and the American Screw Company (mid-19th century, automated production). These machines performed heading, thread chasing, slotting, and pointing in a sequence of automated operations. Patent literature and museum collections (e.g., American Precision Museum) document these designs in detail. See: Rybczynski, W., “One Good Turn”; Roe, J.W., “English and American Tool Builders.”↩︎

29. Self-drilling screws in NZ construction: Self-drilling (tek) screws are the standard fastener for fixing profiled steel roofing and cladding (COLORSTEEL and similar products) to steel purlins and girts. NZ building practice per NZS 3604 and manufacturers’ installation guides specifies self-drilling screws for these applications. NZ’s COLORSTEEL-clad building stock represents hundreds of millions of installed self-drilling screws. See: NZS 3604 (Timber-framed Buildings); COLORSTEEL installation guides; NZ Metal Roofing Manufacturers Association.↩︎

30. Case hardening of self-drilling screws: The drill point and thread of self-drilling screws are typically case-hardened by carbonitriding (heating in an atmosphere containing carbon and nitrogen at ~750–900 degrees C), which produces a hard surface layer (approximately 55–60 HRC) over a tough core (~30–40 HRC). This allows the screw to drill through steel sheet without the screw breaking under the driving torque. The process requires controlled-atmosphere furnace capability. See: ASM Handbook, Volume 4 (Heat Treating); fastener engineering references.↩︎

31. Pack carburising (case hardening): Pack carburising is one of the oldest heat-treatment techniques, in use since antiquity for hardening iron and steel surfaces. The workpiece is packed in a sealed container with carbonaceous material (charcoal, bone meal, leather scraps) and heated to 850–950 degrees C for several hours. Carbon diffuses into the surface, producing a hard case (typically 0.5–2.0 mm depth depending on time and temperature) over a tough core. The process is well-suited to workshop-scale production but case depth and hardness are difficult to control precisely without pyrometry and metallographic testing. See: ASM Handbook, Volume 4 (Heat Treating); Totten, G.E. (ed.), “Steel Heat Treatment Handbook,” 2nd ed.↩︎

32. Washer function: Washers distribute clamping force, reduce bearing stress on the joined material surface, and (for spring washers) provide vibration resistance. In timber connections, washers prevent bolt heads from pulling through the wood under load. AS/NZS standards and NZS 3604 specify washer use for structural timber connections. See: standard structural engineering references; NZS 3603 (Timber Structures Standard).↩︎

33. Washer production tooling: Flat washers are produced by blanking and piercing – two standard press operations. A punch-and-die set for washer production can be made by a machinist from tool steel in a few hours. The die consists of a hardened plate with a round hole (the outer diameter), and the punch is a hardened cylinder that matches the hole. A second, smaller punch produces the centre hole. See: standard sheet metal working references; Machinery’s Handbook.↩︎

34. Bolt grades and heat treatment: ISO 898-1 specifies mechanical properties for carbon steel and alloy steel bolts. Grade 4.6: tensile strength 400 MPa, yield 240 MPa, no heat treatment required (hot-rolled or cold-drawn low-carbon steel). Grade 8.8: tensile strength 800 MPa, yield 640 MPa, requires quenching and tempering of medium-carbon steel (0.15–0.40% carbon with boron, or 0.25–0.55% carbon without). Heat treatment parameters: austenitise at 830–860 degrees C, quench in oil or water, temper at 425–500 degrees C. Resulting hardness approximately 22–32 HRC. See: ISO 898-1; standard heat-treatment references.↩︎

35. Tensile testing capability in NZ: NZ has tensile testing machines at several institutions: University of Auckland (Department of Mechanical Engineering), University of Canterbury, Massey University, AUT, HERA (Heavy Engineering Research Association), Callaghan Innovation, and several commercial testing laboratories (e.g., Metals NZ, SGS NZ). These machines can test bolts to failure and verify grade compliance. See: HERA, https://www.hera.org.nz/; university engineering department resources.↩︎

36. Bolt grades and heat treatment: ISO 898-1 specifies mechanical properties for carbon steel and alloy steel bolts. Grade 4.6: tensile strength 400 MPa, yield 240 MPa, no heat treatment required (hot-rolled or cold-drawn low-carbon steel). Grade 8.8: tensile strength 800 MPa, yield 640 MPa, requires quenching and tempering of medium-carbon steel (0.15–0.40% carbon with boron, or 0.25–0.55% carbon without). Heat treatment parameters: austenitise at 830–860 degrees C, quench in oil or water, temper at 425–500 degrees C. Resulting hardness approximately 22–32 HRC. See: ISO 898-1; standard heat-treatment references.↩︎

37. Bolt grades and heat treatment: ISO 898-1 specifies mechanical properties for carbon steel and alloy steel bolts. Grade 4.6: tensile strength 400 MPa, yield 240 MPa, no heat treatment required (hot-rolled or cold-drawn low-carbon steel). Grade 8.8: tensile strength 800 MPa, yield 640 MPa, requires quenching and tempering of medium-carbon steel (0.15–0.40% carbon with boron, or 0.25–0.55% carbon without). Heat treatment parameters: austenitise at 830–860 degrees C, quench in oil or water, temper at 425–500 degrees C. Resulting hardness approximately 22–32 HRC. See: ISO 898-1; standard heat-treatment references.↩︎

38. Treenails in timber construction: Treenails (also “trunnels”) are wooden dowels used to pin timber joints. They were the standard fastener in heavy timber-frame construction, shipbuilding, and bridge building for centuries before metal fasteners became cheap and abundant. In NZ, treenails were used in early colonial construction and in traditional Māori building. Suitable NZ timbers for treenails include matai, totara, puriri, and rata. Australian hardwoods (if available through trade) are also excellent. See: Hewett, C.A., “English Historic Carpentry”; traditional NZ building references.↩︎

39. Mātauranga Māori fastening and jointing: The structural performance of traditional Māori lashing is documented in ethnographic literature and in the practical experience of the waka hourua revival. Key sources: Best, E. (1925), “The Maori Canoe,” Dominion Museum Bulletin No. 7 — describes waka construction jointing and lashing methods in detail, including strake attachment and outrigger lashing. Pendergrast, M. (1987), “Te Aho Tapu: The Sacred Thread,” Reed Books — covers muka preparation and cord-making. Phillipps, W.J. (1952), “Maori Houses and Food Stores,” Dominion Museum Monograph No. 8 — describes whare framing joints and tukutuku panel attachment. For waka structural lashing under load, see also: Te Toki Voyaging Trust, construction and voyage documentation. The labour-intensity tradeoff estimate (lashing vs. nailing) is a practitioner judgment based on general carpentry experience — the actual ratio depends heavily on joint type, material preparation state, and practitioner skill; no rigorous comparative time-study is known to the authors.↩︎