Re: Bolts, beginner's question.
Posted by MadMike on December 5, 2017, 2:53 pm, in reply to "Bolts, beginner's question. "
mark, 1950's B31/33 would have has BSCY (Cycle) threads. these are mostly 26 TPI but from 7/16 or 1/2 inch diameter some had 20 TPI. The thread form is not compatible with BSW or BSF threads. There is, however, a 1/4 BSF bolt that is also 26TPI. Do not be misled into believing that they are a match: they are not. The thread angle is different and if you fit a BSF nut to a BSCY bolt (or vise versa) at this size you may have them vibrate loose or strip when tightening.
The hexagon sizes on BSCY are the same as BSW, so use BSW spanners. Many of the "Imperial" spanners sold on ebay are in fact AF spanners. If you need any specials, I keep the BSW hex bars in my garage and can turn them up for you. HTH.
Other opinions may be available but this one is always correct.