This piston kit by Silencer Co. contains 5 pistons and three O-ring packs. The kit features .578x28 piston (1) 1/2x28 piston (1) 16mm x 1 LH piston (1) 13.5mm x 1 LH piston (1) and 9/16x24 piston (1). This kit is made to fit the Osprey and Octane suppressors by Silencer Co. Features: 578x28 piston, 1/2x28 piston, M16x1 LH piston, M13.5x1 LH piston, 9/16x24 piston, booster assembly O-ring pack, M13 O-ring pack, M16 O-ring pack