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If you did it up real tight it would give the muzzle some choke like the flash 22lrs :thumbsup:

Looks like it....in your photo it almost looks like the the thread is tapered? or maybe just a trick of the camera.
Regardless if 11mm=11 threads and 12mm = 12 threads it will be 1mm pitch.

Over how many threads? 12mm over 12 threads would be 16x1 if its not that then could be anything especially if done by a home gamer.