Griffin Armament Fixed mounts threads directly into your booster housing and allows you to remove the booster piston, spring, and piston retainer and use this single component on your fixed barrel firearms. Sprung pistons should not be used on a fixed barrel firearm as this will cause the booster assembly to batter itself to destruction. This part saves about an ounce of weight versus running a booster piston and fixed barrel spacer.5/8x24 is a good fit to direct thread to 300BLK subsonic and .357 guns. 1/2x28 would work for 1/2x28 threaded 9mm carbines. Note: This mount is not intended for use on any higher pressure cartridges like 300BLK supersonic or 5.56/.223. FeaturesCompatible with the Optimus, Resistance, and Revolution series of suppressors7075T6 AluminiumFor use on Fixed Barrel firearms