I am currently taking apart a nice old park bench – wooden slats and cast iron supports, that is fitted together with carriage bolts. Unfortunately, due to age, some of the carriage bolts have seized and when you come to remove them they simply spin within the square holes cut into the wood.

Thinking of when it gets painted and varnished I am going to have problems tightening the carriage bolts again. I’d rather not put plain bolts through the wood as these would stick out of the seat and look ugly, is there anything else that has a flat/smooth head and can be used to replace carriage bolts in circumstances like this or is the only option putting some plastic caps over the ends of the bolts ?

unless you replace the wood (so end up with nice new tight holes for the square to key) the bench will go together sloppy again.

Whenever I refurb those kinds of benches I either replace the wood or trim 2″ from each end of the slats so you have new wood for the holes.

Can’t you just replace them with new carriage bolts?

Or am I missing something?

EDIT – Ah right I see now, no the bolts so much as the fitting!

If you are putting new carriage bolts in then you should be able to tighten them up without them spinning just from the friction. It might be a bit tricky to undo next time but that may well be someone else’s problem. You could also use button headed allen bolts and fill the Allen recess but that may result in the same issue

Can’t you just use bigger bolts?

can you run the nut on then grip the protruding shaft and tighten up that way?
Bit agricultural, but it’ll not need pulling apart again for a good few years…….

Or you could just fill the hole around the bolt with a mix of resin and sawdust (araldite maybe) and tighten up once it’s hardened, bit permanent tho.

If you are intending to use new replacement carriage bolts all you need to do is ensure that the nut run up the threads easily, use a plain washer between the nut and cast iron frame and you should be ok.

Large button head hex socket screws.

There has been some progress and I’ve taken the advice to cut down the ends slightly. Replacing the wooden slats would have been better advice to take as it has taken a lot of work to dismantle the bench cut the slats down and sand them back to good wood. The wood being surprisingly good – the benches were originally used for the Gateshead Garden Festival in 1989 and have been with us since they were auctioned off. When they made them they made them well.

Before:

During – there is good wood under there, teak ?

The slats are in the process of getting some Osmo wood stain on them…