SilencerCo pistons are designed for easy replacement to fit different host firearms or calibers. They are made from 17-4 stainless steel and heat-treated for maximum durability. The piston is part of the Nielson device, which moves to enable semi-automatic cycling and unlock pistol barrels. Use a Fixed Barrel Spacer for fixed barrel setups. SilencerCo pistons feature female threading that connects to SilencerCo threaded barrels.