All of our adaptors use M8 locking screws except for the Shopsmith
adaptors, they use the standard shopsmith locking screw size which is
imperial.
Metric screws are typically specified by the major diameter and the
length which is really dumb as the pitch is not part of the
designation, but our set screws are all coarse pitch, fine pitch
metric screws are quite uncommon.
Set screw locking is starting to get to be a real mess as companies
are building spindles with accomodations for set screw locking but
which are peculiar to their own machines.
When we built our machines many people knocked us for using an M33
spindle instead on an 1-1/4 but we duplicated a spindle size that was
already out there and had a good locking groove design.
regards
Kevin Clay
Oneway Manufacturing