CGS Group Piston Features The CGS Pistons for the Kraken MOD9 and Nautilus series silencers allow the user to attach the silencer to any firearm that has barrel threads matching the piston threads. This piston system is also self aligning and the piston itself has a very positive spoke lock to the housing. CGS Group Piston Specifications Model: Piston Finish: Black Nitride Material: 17-4 Stainless Steel Length: 2 Thread Pattern: 1 / 2-36 tpi Weight: 1.30 oz