Hi, As this 'threading tool' thread has progressed a wee bit off the thread,please let me indulge. When machining threads (or plain diameters for that matter)there is a tolerance standard that should be followed,that way, if I cut a thread (or a diameter) here in Scotland, it will fit a thread or diameter machined to the same tolerance standard in U.S.A.
A perfectly formed external thread will not fit a perfectly formed internal thread(two perfect sizes cant fit) that is why we have tolerances, -minus for external, and +plus for internal. Generally imo 55 and 60 degree threads should not be mixed up and never mixed on coarse threads, say upward of 6 t.p.i. or 4mm metric pitch, simply because the effective diameters of the threads will be wrong. However,as in the case of finer threads,I think 12 t.p.i. was flagged up at the start of this exchange,(thread) the depth of a 12 t.p.i.thread being approximately .053" and AR Gunsmiths having both external and internal threads to hand at the Lathe, the mixing of 55 degree (Whitworth) and 60 (Unified) the angle difference would be absorbed by the + and - tolerance needed to allow the threads to fit, so would therefore, make very little difference to the fit of the thread. Hope this helps,good luck.jc

quote:

Many companies make 55 degree inserts. I guess I'm old fashioned, I still use HSS and grind my own.

Mike McCabe Licensed Firearms Manufacturer

Mike makes his little kids grind his HSS bits. If they do a good job he does not make them eat their peas or Brussel sprouts at the evening meal. He even bought them ice cream once when they nailed the angle, depth and pitch just right.

I read Voltaire's biography once; it was simply shocking.

I put Trax and J.D. on ignore. This post shrank to 1/3 of a page long.