I have Deore cranks with an on one ringmaster (narrow/wide) ring but my singlespeed chainring bolts are barely long enough to fit. What size should I go for?

I know it’s obvious, but the ring holes aren’t countersunk on one side, are they?

Try a double bolt off another chainset?

Ringmasters are so fat that the standard bolts that would fit a middle/outer ring combo will do. Go and find them! (assuming you are converting from a double/triple) 🙂

tbh, on-one should advertise this fact as it would stop folk spending money on unnecessary bolts.

Cheers. I think that standard is 10mm so ordered a pack of those, should do the trick.