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.TheMOD9 has 12 index points for the piston(for adjusting point of impact shift)and has special porting on the piston to help limit first round pop.The piston system on the MOD9 works so that at anypoint in the recoil cycle,6 of 12 spokes are always keeping the piston aligned while the other 6 are sliding over the ports in the housing.This piston system is also self aligning and the piston itself has a very positive spoke lock to the housing.