The RRA 9mm Compensator is just what you need to complete your detachable magazine OLL build. Combine this with a MonsterMan Grip, 9mm stock spacer, and an A2 fixed stock and you can actually use detachable magazines! 1/2″x36 thread. This brake does not come with a crush washer. Be sure to order one if you don’t have one in order to attain proper indexing.