> Typically,the standard Joss pin is a true 5/16,in MOST cases,the Schon is .010 undersized on both the outside or major diameter,and down at the bottom of the thread groove,or minor diameter. The ONLY true way to measure,is with a micrometer,and either a thread mike,or thread wires,using the 3-wire method. Trust me,I've miked both.
I got a new Joss shaft for my Joss SP break cue once,and the insert was too tight for both my Joss AND my Schon. In my experience,Schon is much more consistent with the fitting of their inserts,even though Evan has been known to experiment with his pin threads in order to make it harder for other cuemakers to replicate the same quality of fit.
I've never even heard of a 5/16-14 tap with different H limits for size and thread fit,so indeed a standard tap ran back and forth about twice should make it fit. Tommy D.