@ Freeriderz:
I don’t have such with me (S21A) but from justanotherguy if it has .75mm pitch (eyeballing it), I be looking at 3/4” x 32 TPI Left Hand. That’s closer to .75mm than 28 TPI.
BTW, all 24 or 32 TPI are standard on inch stock bar. But a better way to check pitch is against a known screw. Doesn’t matter the size, just if the threads mesh*. OD of threaded part is always some .005 to .008” less than nominal (sometimes much more for sloppy fit).
EDIT: * Oops – Left-hand thread can’t mesh stock screws (right hand). But check if crests line up.