They get mixed up constantly — on the phone, on site, in the search bar. Both are chunky timber fasteners with "coach" in the name, but a coach bolt and a coach screw are two different tools for two different jobs. Pick the wrong one and you'll either strip the head or leave a joint weaker than it needs to be.

Here's the short version, then the detail:

Quick reference — coach bolt vs coach screw

 

Coach bolt (carriage bolt)

Coach screw (lag screw)

How it fixes

Goes through the timber, held by a nut and washer on the other side

Screws into the timber — no access needed behind

Head

Domed head with a square neck underneath that stops it spinning

Hex head — driven with a spanner, socket or impact driver

Pilot hole

Drilled clearance hole only

Pilot hole recommended, especially in hardwood

Best for

Gates, door frames, structural timber-to-timber joints you can reach both sides of

Gate posts, decking frames, landscaping timber, fixing into existing timber

Standards

DIN 603 (bolt), DIN 934 (nut)

Hex head lag screw

We stock

M6–M12, zinc plated, stainless or galvanised, nuts included

M6–M12, zinc plated & A2 stainless

Coach bolts — the through-bolt with the anti-spin neck

A coach bolt (also called a carriage bolt or cup square bolt) has a domed head with a square section underneath. You drill a clearance hole, push the bolt through, and that square section bites into the timber to stop the bolt spinning while you tighten the nut on the other side.

That makes coach bolts the choice when you can get at both sides of the joint: gate hinges and stops, door frames, bolted timber connections where you want a smooth, tamper-resistant dome on the face and a proper nut-and-washer clamping force doing the work.

What we stock: coach bolts M6–M12 in zinc plated, stainless steel or galvanised — and every pack comes complete with nuts, so there's no second trip to the fixings bin. Conform to DIN 603 (bolt) and DIN 934 (nut).

Shop the range: Coach Bolts — nuts included

Coach screws — the heavy-duty timber screw

A coach screw is essentially a big, brutal wood screw with a hex head. You drive it straight into the timber with a spanner, socket or impact driver — no nut, no through-hole, no need to reach the back of the job. That's the whole appeal: one-sided fitting.

Where it earns its keep: fixing gate posts to boards, securing decking joists and frames, landscaping sleepers, play equipment, attaching anything heavy to existing timber where you can't get behind it. Because the thread bites deep along the whole shank, a coach screw in sound timber holds remarkably hard.

One tip that saves stripped heads: drill a pilot hole — a touch smaller than the shank in softwood, closer to the shank in hardwood — and drive at low speed. Hex heads are tough, but they're not immune to rounding off if you battle a full-depth screw in un-drilled hardwood.

What we stock: coach screws M6–M12, zinc plated and A2 stainless steel, for timber-to-timber and metal-to-timber use.

Shop the range: Coach Screws (Lag Screws)

Choosing by job

  • Garden gate on a timber post: coach bolts through the post for the hinges and stop; coach screws for anything you're fitting to the face only.

  • Decking frame: coach screws to build the frame and fix joist hangers' timber; coach bolts on any structural joint where both sides are accessible.

  • Sleepers and landscaping: coach screws for speed on the face; galvanised coach bolts where soil contact means you want the heavy finish.

  • Play equipment and structural joints: coach bolts — the nut-and-washer clamp and anti-spin neck is the right engineering for anything that moves and takes load.

  • Fixing to an existing wall or fence you can't get behind: coach screws, every time — there's no way to fit a nut.

Which finish?

  • Zinc plated — the everyday choice for internal and sheltered use.

  • Galvanised — outdoor jobs with weather exposure; the thicker coating handles the wet British year-round.

  • A2 stainless steel — coastal, wet and long-life jobs where rust streaks on timber would spoil the finish (and stainless coach screws won't).

Not sure which fits the job? Call the team on 01270 252 326 — lines open Mon–Fri, 8am–4:30pm. With over 25 years supplying the trade, we can size a coach bolt or coach screw for whatever you're building.

Fastco Fasteners & Fixings — trade prices on screws, nuts, bolts and fixings, with fast UK delivery.