3/4" x 20 BSCY & 3/4" x 20 UNEF/UNS (haven't got the info to which one is which at hand at the moment) both have a 60 degree thread angle. The difference is the depth mainly. BSCY is shallower by a few thou, plus the bottom of the 'v' is more rounded. This is the difference in a nutshell , the exact specifics are available.