Fixings & fasteners: load and exposure decide every choice

The fastener is the cheapest part of any connection and the one most likely to fail it. Two questions decide every choice: how much load the joint carries (which fixing, what size, how many) and how corrosive the site is (which coating or material). Get either one wrong and the connection lets you down.

Two questions before you order

Every fixing decision comes back to load and exposure. On the coast a bright or lightly-galvanised nail bleeds rust in a year; inland it’s fine. So the exposure zone drives the spec as hard as the load does.

• Load — which fixing, what size, and how many.
• Exposure — the coating or base material that survives the site’s corrosion risk, from sheltered inland to Zone D coastal.

Nails

Galvanised is the NZ default for anything outdoors; bright and electro-galv are indoor-only. As the coast gets closer you step up to stainless.

• Common bright nail — steel, no coating. Indoor framing only; corrodes fast outdoors. Rarely used in NZ, as galv is preferred everywhere.
• Hot-dip galv nail — zinc coating around 50µm, applied after forming. The standard NZ outdoor nail for Zone A/B exterior work: decks, framing, fencing. Marked ‘HDG’ on the box.
• Electro-galv (electroplated) — a lighter zinc coating, roughly 5–15µm. Indoor or very-low-exposure only; rusts fast outdoors.
• Stainless steel 304 (SS304) — 18% chromium, 8% nickel; austenitic and non-magnetic. For Zone C coastal, and Kwila/Cedar where the tannin corrodes galv. Pricier.
• Stainless steel 316 (SS316) — adds 2–3% molybdenum for the best marine corrosion resistance. For Zone D coastal, geothermal areas (Rotorua, Taupo) and pool surrounds. Most expensive.
• Type 17 collated nail — hot-dip galv ring-shank with a type-17 cutting point; 50×2.8 to 100×3.75 are common. The standard NZ framing nail through a nail gun, with the ring shank giving better grip.
• Lost-head / bullet head — a small head that punches below the surface and fills with putty. For skirtings, architraves and MDF where you want an invisible fix.

Screws

Screws are faster and stronger than nailing, and there’s a purpose-made screw for most fixing jobs.

• Type 17 wood screw — Phillips, Robertson or square head, hex-flange or countersunk, with a self-drilling tip that cuts as it goes. For decking, framing and anywhere a nail used to go.
• GIB Grabber HighThread 32×6g — self-drilling thread, bugle head. For plasterboard fixing: 300mm perimeter centres, 12mm bound edge, 18mm cut edge.
• GIB Grabber 41×6g — a longer GIB screw for 13mm Braceline/Fyreline and double-layer fire-rated work.
• Type AB self-tapping (Tek screw) — drills its own hole into steel; hex head with a neo washer. For sheet metal to purlin (roofing, cladding), to the NZ Metal Roof Code of Practice spec.
• Coach screw / lag bolt — M8–M16 hex-head wood screw. For stringer-to-house, bearer-to-pile and structural timber connections. Pre-drill a pilot.

Bolts & chemical anchors

When the connection is structural and needs to be proven, you move to bolts and anchors — sized, graded and coated for the job.

• Hex bolt + nut + 50×50×3 washer — M8–M16, grade 4.6 or 8.8, hot-dip galv or stainless. For bearer-to-pile and anchor-pile connections (12 kN required in both directions).
• Cup head bolt — a coach-bolt with a square underhead that stops it spinning. For through-bolting timber where the square hole is the NZ tradition.
• Trubolt / wedge expansion anchor — a wedge-type expansion anchor, e.g. Ramset Trubolt or Hilti.