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Coach Screws

Coach Screws

Coach Screws

Not sure what screw size you have or need?

Two ways to confirm before you order - whichever you already know.

1If you have a screw in hand

Measure across the outside of the thread - not the shank - to get the gauge (an 8g screw measures about 4.2mm). Screw gauges have a wider tolerance than bolts, so treat it as a close match rather than exact. Then measure the length - countersunk timber screws are measured overall, head included.

Open the screw gauge sizing chart ›

2If you know the gauge

Every product page carries a Screw Gauge and TPI chart for its range - every gauge links straight to the product. Rule of thumb for timber: coarse threads for softwood and framing, fine threads for hardwood.

T17 timber screw side profile showing where to measure

T17 timber screw - gauge is measured across the thread.

Coach screws (lag screws) are heavy hex-head screws that thread directly into timber to make a strong structural connection - bearers to posts, pergola joints, fence rails, brackets and framing. Unlike a wood screw they are driven with a spanner or socket on the hex head, and a pilot hole is drilled first so the coarse thread bites without splitting the timber.

Coach screws are also listed under our Bolts category - they are the same product, browseable in both places.

GRADES AND MATERIALS

Stocked in hot-dip galvanised and zinc-plated carbon steel. Galvanised is the right choice for outdoor and treated-timber framing; zinc suits dry interior work.

DRIVE AND INSTALLATION

External hex head driven with a spanner or socket (match the AF across-flats). Always drill a pilot hole about 70 percent of the shank diameter into the receiving timber - this lets the thread pull in without splitting and gives full holding power.

SIZE AND THREAD

Diameters M6 to M12, lengths from 25mm to 150mm-plus. Coarse coach-screw thread for maximum bite in timber. Size the length so the thread fully engages the structural member behind the joint.

WHY AUSTRALIA TRUSTS BOLT & NUT

With 15+ years selling fasteners online from Brisbane, we hold over 25,000 stock lines and 200 million pieces - 98.75% of online orders placed before 1pm leave same day. Save more as you buy more - we offer up to 13 price breaks plus 3 spend-tier discounts. Read our customer reviews or get in touch if you need help picking the right coach screw.

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