OK, I think I’m missing something here.
Yes its fine if you thread a 1/4″ bar with a 1/4″ BSW die as its 20TPI, and it screws into the 1/4″ Clarkson collet perfectly.
However if I need to use a 3/8 or 1/2″ bar, and collet, the TPI is 16 & 12 respectiveley.