Square Coach Bolts with Hex Nut Zinc Plated M6–M16

Square coach bolts are one of those fixings that have been doing the same job reliably for a very long time, and for good reason. Each bolt features a domed round head with a square shoulder directly beneath it. When the bolt is driven into a pre-drilled hole in timber, that square section bites into the wood and stops the bolt rotating as you tighten the nut. No need to hold the head with a spanner — the timber does the work for you. These zinc plated square coach bolts are supplied complete with a hex nut and are available across a wide range of diameters and lengths to suit most structural and general fixing jobs.

The zinc plating provides a reasonable level of corrosion resistance for general construction use. These bolts are suited to covered or semi-exposed conditions — think structural timber frames, external joinery under cladding, or workshop and agricultural building assembly where the fixing is sheltered from direct weathering. The finish keeps rust at bay during installation and through normal service conditions, without the premium cost of hot-dip galvanised alternatives.

Where Square Coach Bolts Are Used in Construction

Square coach bolts are a staple fixing in timber-frame construction, fencing, gates, playground equipment, and general joinery. The clamping action of the domed head and nut makes them well suited to through-bolting two or more timber members together, or for attaching brackets, hinges, gate furniture, and other ironmongery to structural timber. Because the square shoulder locks in flush with the timber face, the domed head sits neatly on the surface without any protruding edges that would foul surrounding materials.

These bolts are fully threaded up to and including 150mm in length. From 160mm onwards, the bolt is partially threaded, with a plain shank running from beneath the square shoulder. This matters on longer lengths: the unthreaded shank passes cleanly through the timber without binding, while the threaded section engages the nut on the far side. It is worth accounting for this when selecting length, particularly when clamping thick timbers or stacking multiple members.

Choosing the Right Size

This range covers M6 through to M16 diameter, with lengths from 20mm up to 300mm. As a general guide, M8 and M10 are the most common sizes for general joinery and light structural work, while M12 and M16 are typically used where higher shear loads or heavier section timber is involved. Always allow enough thread engagement beyond the nut for a washer where load distribution across a softer timber face matters. Box quantities range from 5 to 200, so whether you need a small bag for a one-off job or a bulk quantity for a larger project, there is an option to suit.

Each pack includes a matching hex nut. A flat washer under the nut is recommended where timber is soft or where the nut might otherwise pull into the grain under load. These square coach bolts offer a straightforward, cost-effective solution for the kind of heavy-duty timber fixing that comes up on almost every construction or joinery project.