The Guarder Ver. 7 Cylinder Head is made from high quality S303 Stainless Steel and is designed to fit the Tokyo Marui Ver. 7 gearbox. The Guarder series of upgrade parts are compatible with most major brands of AEG. Guarder goes above and beyond companies like Systema and Prometheus 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.