Ok, I confess something: I have no idea what size wrench fits on a No8 nut. Yes, yes, I know, stop laughing. But seriously - no socket or wrench (imperial) among the hundreds I have lying around fits a No8 nut. For decades I have always resorted to a 9mm . It's not 11/32" (big)and it's not 5/16" (small) . There is no consensus on this on the interwebs. Wrench sizes suggested vary from 1/4" to 3/8". I have plenty of 9mm sized sockets and wrenches plus a few I custom ground to fit. But what is the proper size? 21/64"??