These pistons were designed to be easily changed for different host firearms or calibers. Pistons are built with 174 stainless steel, then heat-treated for maximum durability. The piston is part of the Nielson device that moves and allows semi-automatic cycling for unlocking pistol barrels. Throw a Fixed Barrel Spacer on for fixed barrel applications. SilencerCo pistons have female threading that attaches to their SilencerCo threaded barrels. XL pistons are for firearms where the silencer requires additional length between the threaded barrel and the silencer. Compatible with Omega K Series Hybrid 46 Hybrid 46M Osprey Series Octane Series Omega 36M