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Mills Bomb Base Thread Info?


Well-Known Member
Hi All, Can anyone who has done restoration work on mills related items tell me the thread details for the hole in the M36 base plug?? the hole the gas check screws into??
I have a job underway involving cutting a couple of threads to fit the base plug but Im having trouble getting an ID on the thred as its an odd one and the sample thread I have is a bit worn to measure correctly.
So if you can help with TPI,pitch,dia it would be of great assistance

Best Regards

Mills threads

For the majority of No.23 base plug holes for rifle rod and all No.36 MkI base plug holes for gas check, the required tap size is 9/32" 20 tpi BSW form, though when rethreading it's important you get a plug tap, rather than taper or second cut.

The less common Morum No.5 threaded base plugs (and some No.23 MkIs) use a standard cycle thread of 5/16" 26 tpi.

For completeness, should you want to rethread the No.5 or Nos.23 MkI & II filler holes the thread is 7/16" 20 tpi BSW form, and for the No.36 is 9/16" 20 tpi BSW form.

Finally the base plug thread is 1.25" 20 tpi BSW form.