The Madbull Standard Cylinder Set has all the necessary parts to upgrade or replace the cylinder assembly in your gearbox. The Cylinder Set includes a cylinder head, air seal nozzle, Madbull Alien green PX piston, the cylinder, and a polycarbonate mushroom piston head w/ bearings. The Cylinder set is compatible with most major brands of AEG. Take your standard gearbox to the next level of performance with the Madbull upgraded cylinder set. It is a must have for a high quality build.