Garand gas cyl and lock screw thread sizes

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.

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Originally Posted by purple

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.

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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.