barrel threading

In firearms, barrel threads refer to the screw threads used to attach a barrel.
Action threads, also called receiver threads, are situated at the chamber end of the barrel, and can be used for attaching the barrel to the receiver. The receiver normally has corresponding threads which are internal, with the matching action threads on the barrel usually being external threads. This design is most commonly used in rifles and revolvers, but also on some pistols and shotguns. This method of fixing a barrel to a receiver has been used extensively by firearms manufacturers since before the 20th century, and can be viewed as a traditional barrel mounting method. Action threads are not the only method of fixing a barrel to a receiver (see Alternative methods below). Furthermore, some firearm designs have moving instead of fixed barrels (e.g. most recoil operated pistols or the Barrett M82 rifle).
Muzzle threads are situated at the muzzle end of the barrel and can be used for mounting accessories such as a flash hider, suppressor or muzzle brake (compensator).

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