AIP Piston Head For Marui 5.1 / 4.3 / 1911 GBB - Replace the original plastic Piston head of airsoft pistol - With O-ring (FKM) - Suitable for Marui 5.1/4.3/1911 Series Airsoft Gas Blow Black GBB Pistol - As always, upgrading GBB require necessary skill & technique, consult expertise if needed