The Bravo Ver. 2 Cylinder Head is made from high quality Aluminum and is designed to fit the Ver. 2 gearbox. The Bravo series of upgrade parts are compatible with most major brands of AEG. Bravo is following the footsteps of Guarder by providing a cylinder head with 2 o-rings instead of just one. The extra o-ring provides a much better seal against the cylinder for maximum compression.