H.S.S. 6-80 taps are very rare. They are designed to tap holes for 6-80 micro precision threads. These threads are used by knife and gun makers to create a maximum adjust threading, or to create a thread that is less prone to "back-out", a common issue with coarse threads.
Try a 6-80 thread on your next project and you'll never go back, or back-out again!!!
Thread - 6-80
O.A.L. - 2"
Threading - .75"
Pilot Drill Needed = .125"