Thanks for this; have done and as everyone rightly guessed it was M5 (why don't they just match the hex sockets to the bolt?) but I've now gone and cross threaded the damn eyelet with an alu bolt which I got about halfway in before realising it was well and truly stuck. I imagine tapping it would further compromise the already weakened thread material so am thinking of chasing it through from the back; are there any better ideas? Alternatively I can just leave it all alone given that the P-clamps work fine, but feels like an imperfect solution.
I doubt you will have done much damage to steel threads with an aluminium bolt. Your suggestion of chasing it through with a tap from the back side is the best option.
Thanks for this; have done and as everyone rightly guessed it was M5 (why don't they just match the hex sockets to the bolt?) but I've now gone and cross threaded the damn eyelet with an alu bolt which I got about halfway in before realising it was well and truly stuck. I imagine tapping it would further compromise the already weakened thread material so am thinking of chasing it through from the back; are there any better ideas? Alternatively I can just leave it all alone given that the P-clamps work fine, but feels like an imperfect solution.