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Cup Head Coach Bolts
Measure the thread diameter, or the square section directly under the dome - its width matches the bolt size (an M10 cup head has a 10mm square). Our visual guide confirms size, pitch and length.
The nut on a cup head bolt is a standard hex nut. Match your spanner / socket AF (across-flats) to the size it fits - our reference chart covers every metric and imperial size we stock.
Cup head coach bolts — also called carriage bolts — are used to fix wood to wood or wood to steel with a matching nut. The bolt has a low-profile domed head and a square section under the head that bites into the timber and prevents the bolt from spinning when the nut is tightened.
Because the head locks itself, you can install a coach bolt from one side and tighten the nut from the other without holding the head with a spanner — useful for blind-side timber assembly.
MATERIALS AND FINISHES
Galvanised — Hot-dip galvanised Class 4.6 for outdoor timber, decking, fencing and treated pine.
A4-70 G316 Marine Grade Stainless — For marine and coastal timber work where galvanising won't last.
A2-70 G304 Stainless Steel — General-purpose stainless for protected external timber work.
GRADES STOCKED
Class 4.6 — Low-tensile galvanised, the standard for general timber-to-timber and timber-to-steel.
A2-70 / A4-70 Stainless — Stainless equivalents for corrosion-prone environments.
Sizes: M6 through M20 metric (M12, M10 and M8 are the busiest); imperial 1/4", 5/16" and 3/8" in UNC.
Thread systems: Metric Coarse and UNC.
Standards: AS1390:1997 & AS1112:2000, DIN 603 (metric), ANSI B18.5 (imperial).
Always pair with a flat washer under the nut to spread the load on timber. Pre-drill clearance holes — refer to our Technical PDF's Library for sizing.
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 bolt.
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Domed-head bolts with a square neck that pulls into the timber and stops the bolt turning as the nut is tightened - no second spanner needed. Also known as carriage bolts. Galvanised Class 4.6 and A4-70 G316 stainless.
TECHNICAL RESOURCES
Key charts and specification sheets: Imperial vs Metric Strength Chart · Bolts Markings · Specs - Cup Head Bolt Nut Metric Coarse Galvanised AS1390
For the full library, see our Technical PDF's Library.
