This muzzle brake is a scaled up copy of a real '74 Brake. It's threaded to fit the factory threads on the 12 and 20 gauge shotgun barrels. They are marked "U.S.A." or "Made In USA" and count as a compliance part. They are designed to work with all loads from slugs to shot.
Whether you use my front sight blocks or not, I recommend wrapping the barrel threads with teflon tape to help index the brake. It will ensure you have a nice snug fit when it's indexed. It's cheap and isn't affected by heat from normal firing.