Coach bolts without the square bit under the head

That would be the way nature intended. The square section then stops the bolt turning.

Otherwise, and since they're unlikely to turn, I'd shove them in the lathe and reduce the square shank to the round. I don't think they do blind headed coach bolts without the square boss so you're left with modifying what there is (cue someone with a webpage listing every last size!)

If you do turn off the square bit and blacking isn't intended, Screwfix has stainless steel ones. I've used them in my shed where the fasteners go through the wall.

Some bolts have the square bit, but not IME coach bolts. Might you need to get the terms right? There should be a chart out there showing various bolt types.

IIRC - and I may well not - you can get a black finish by dropping a red hot iron bolt into oil.

NT

And here it is:

OTOH the OED (draft addition 1997) is with the OP and others: "coach bolt n. a large bolt for fastening wood, having a square collar below the head to prevent it from turning as the nut is tightened on it."

I think these are what the OP is looking for:

How do you stop it turning while tightening? For that you'd likely need a fine thread - not usual on this sort of thing.

metric.

The bolts you require are called Roofing Bolts.

They have slotted heads, which the OP stated that he didn't want.

"Bright zinc plated, _cross-head_ roofing bolt complete with square nut."

I too worry about how you'll do the nut up without them spinning. I'd go with a square slot in the bracket.

And I've seen the red-hot-into-oil finish - I used to live next door to a toolmaker.

Andy

Well as there's no such thing as a bolt without a tool fitting in the head so you can do it up and undo it he'll just have to make do won't he.

Yes we all know very well thank you. That's the bit (the square section) that fulfils the function of a tool fitting and which the OP is trying to do without which as I say is not normally made. I fail to see why the presence or absence of a slot in the bolt head makes a blind bit of difference to the functionality of the repair. The square section under the head of a coach bolt actually is a tool fitting. Once the nut has been undone enough to allow the bolt to clear the workpiece you can apply a wrench to the square if the nut is rusted to the remaining end of the bolt. Otherwise there is no way to remove the nut if it's rusted in place than applying uk.d-i-y's favourite tool - all together now - the angle grinder.

But the OP indicated there was probably a bit more than functionality at stake here. Or did you miss "These are for a restoration project"?

In message , Robin writes

I actually acquired a quantity of these bolts at a farm sale. I have gradually used most of them for construction jobs, generally by welding to an angle iron bracket.

I have no idea what the original intended purpose was. They are slightly tapered under the head which may be a forging issue or grip when hammered into a tight hole.

Too large for the OPs purpose; around 5/8ths dia. and 9" or so long.

regards

My guess is coach bolts with a square would be just fine looks wise - except that they are having to fit some form of steel reinforcing plate. And making a square hole in that is too much extra work.

Thanks to everybody for all the useful replies. Just a bit of clarification. I said was a restoration project. It is - it's an old farm cart that sits in the back garden under some trees. It's probably 100-years old, the wooden bits are pretty rotten although just about hanging together. I've replaced some of the easy bits wood with new oak. Most of the iron & steel bits are sound apart from surface rust. The original coach/cariiage bolts, whatever they're called, had no square under the heads. Although not necessary the threads were full length. The nuts were square and rusted solid to the bolts - I had to cut them off. Given their age they would have been "natural" black finish.

This cart is never going to move again, it's just a sort of garden ornament. I'm just trying to give it a few more years life before it ends up on the bonfire! As for the original bolts "not being metric" - well the cart is in the garden of my French home! It's a French farm cart so goodness knows what size/type the threads are. So in the absence of any readily available bolts of the exact form, I'll use standard coach bolts. I'll file a square into the steel/iron bracket and paint everything matt black. It will look OK!

Thanks again.