Advanced Armament Corporation Illusion 9 Piston 1/2x28 TPI Matte Black. All that is necessary to convert the silencer to be compatible with a different barrel thread pitch is to select the proper piston and replace the existing one residing in the rear of the sound suppressor. All AAC pistons are constructed of heat-treated stainless steel with a bead blasted matte finish and each is engraved to indicate the thread diameter thread pitch and direction of rotation for installation. Specifications for Advanced Armament Corporation Illusion 9 Piston: Manufacturer: Advanced Armament Corporation Fabric/Material: Steel Color: Black Finish: Matte Package Contents: Advanced Armament Corporation Illusion 9 Piston Advanced Armament Corporation 64246: Illusion 9 Piston 1/2x28 TPI Matte Black