Two Old Designs, One Modern Problem
Square-head bolts and coach bolts were the standard fasteners of their eras — which means they're all over the equipment that's still working sixty years later, and mostly gone from the shelves that supply it. Forged replacements exist in a handful of stock sizes; everything else is a "call for quote" that assumes production volume.
Square head bolts
Four flats instead of six — more wrench contact, easier to hold in a tight recess, and period-correct on legacy machines.
- Any across-flats and head height — matched to your original
- Machine bolts, setscrews and tap bolts, full or part thread
- DIN 478/479/480 forms and the non-DIN sizes in between
Coach / carriage bolts
Dome head, square neck beneath — the neck locks in a square hole so you can tighten the nut single-handed.
- Neck width and length sized to your existing hole
- Oversize necks to restore grip in worn square holes
- Long and extra-long lengths that catalogs never stock
The Matching Problem, Solved by Machining
Forged square bolts come out of a die: fixed head sizes, standard threads, tooling charges for anything else. That's the right economics for a pallet of new-build hardware — and exactly wrong when what you need is eight bolts that match the twelve still on the machine.
We machine each bolt from bar, so the head is milled to whatever across-flats your wrench, recess or original demands, and the thread is cut to whatever the old nuts carry — metric coarse or fine, UNC/UNF, or BSW/BSF Whitworth gauged from your sample. No die, no minimum, no "nearest available size".
Where They're Needed
Legacy Machine Tools
Square-head gib screws, clamp bolts and way bolts on lathes and mills still earning their keep
Agricultural Equipment
Coach bolts in implement timber and channel — odd lengths, worn holes, missing nuts
Traction & Vintage Vehicles
Whitworth-threaded square bolts, period-correct heads and self-colour finish
Timber Structures
Long coach bolts to your exact grip length, with square nuts and plate washers
Industrial Restoration
Matching the original hardware on pumps, presses and mill equipment
Materials & Finishes
| Option | Detail |
|---|---|
| Carbon steel | The period-correct choice — supplied plain ("self-colour"), black oxide or zinc plated |
| Alloy steel 42CrMo4 | Where the joint carries real load — hardened and tempered, ~10.9 equivalent |
| Stainless A2 / A4 | Outdoor structures and marine timberwork, no rust streaks down the wood |
| Brass / bronze | Decorative and heritage marine work |
| Matched square nuts | Same thread, same across-flats family, same finish — shipped as a set |
Restoring something and the thread is a mystery? Send one bolt. We gauge it (it's usually BSW on pre-1960s British equipment, UNC on American), measure the head and neck, and machine the batch to match — see obsolete fasteners and replacement bolts from a sample.
Will it fit? Square head and coach bolt checks before you order
A square head only works if it sits in the recess or against the stop that holds it from turning, and the across-flats of a new forged bolt seldom matches an old machine. A ½″ BSW square head is 0.82 in — 20.8 mm — across the flats; the nearest metric, M12 at 19 mm, rattles in the recess, and M14 at 22 mm will not go in. The same applies to the square neck of a coach bolt: it must fill the square hole in the timber or the plate, or the bolt spins the moment the nut is tightened.
What do I need to fit a coach bolt in an old timber hole?
A bolt whose square neck matches the hole across the flats, a thread and length that reach through the timber and the nut with two threads to spare, and the head shape — cup or square — that the original had. Send the old bolt or the hole size and the timber thickness.
Same square bolt, but longer, in brass, or a Whitworth thread
A longer shank for thicker timber, brass for a heritage boat, A4 for an outdoor structure, a BSW thread to match the nuts still on the machine, or a head milled to a non-standard across-flats — each is a variant of the same drawing, one piece and up, quoted in 12 hours.
Frequently Asked Questions
Forging needs die tooling and volume; machining from bar gives any across-flats, any thread including obsolete ones, and no minimum — the right economics when you're matching existing hardware rather than buying bulk.
Yes — send one bolt or its dimensions and we machine the head to the same across-flats and height, not the nearest catalog size.
Yes — neck width and length to your hole, including slightly oversize necks to restore the lock in worn square holes. Long and extra-long lengths included.
Yes — BSW, BSF, UNC/UNF and pre-metric machinery threads, gauged from your original so new bolts fit old nuts and tapped holes.
Yes — machined to the same thread and finish, shipped as a matched set, including period plain or black finishes for restoration.
Get Square Bolts Quoted
One sample bolt or the dimensions. Engineers reply in 12h.
// Qty & price
1 pc
Sample price
Confirm fit before a run
10–50
Unit price drops
Setup cost shared
100+
Best price
All tiers quoted upfront
- →No distributor — you pay the maker directly
- →CAD saved after first order — reorder anytime at lower unit price