on that gipsy (5/16" and/or the larger 10mm). I'll have to email the folks at SL Spares...it had never occurred to me that chain type --proof coil and BBB-- might mean they're both compatible with the gipsy.

They'd probably know. But that means, presumably, that I'd need to know *exactly* what kind of chain I have. I know it's 5/16", but beyond that I know nothing...except that it's old (20 years or so?) since it came with the boat (but is in very good condition)...more than likely, it's some out of date chain type ! ;-)