What sort of shackle is used to attach a standard forestay to the ring in the mast (i.e. eyes at both ends)? I have a box of assorted shackles and don’t know which one to use. I obviously have to use the right one for the correct tension.
Pick one that is reasonably strong and won’t rattle undone in the wind.
The forestay shouldn’t be particularly tight – it’s basically only there to keep the mast upright when you don’t have a foresail on the boat, so the shackle doesn’t have to be capable of taking huge loads – but it’s too high up for you easily to keep a regular eye on it, hence the need to use something that won’t work loose while you’re looking the other way. Ours is (I think) something that seems to be called a rigging clip, rather than a true shackle.