Quote Originally Posted by purple View Post
A question for the machinists on thread compatibility. I have a 9/16-32NS tap which I use to clean up the threads on gas cyls. The Kuhnhausen Shop Manual indicates that gas cyl threads are 9/16-32 NS3B mod, major dia .5625; minor dia .532+.003. Thread sizes on the lock screws are shown to be 9/16-32 NS, major dia .5625 min; minor dia .5287+ .0034.

As I read it I should be OK to use my 9/16 -32NS tap to clean up the threads on several lock screws which either won't fit or which bind part way thru installation. Can someone confirm this pls.
Yes. The gas cylinder thread minor diameter is slightly larger that the lock screw minor diameter. Otherwise if they both were the same, it would be a metal-to-metal fit on the minor diameter. I use a 9/16-32 NS HS3 tap which is .0025 oversize overall. You won't know the difference cleaning buggered and dirty threads.