The Dual Fuel Fill adaptor is unique to the Discovery Series product line. This adaptor comes complete with a CO2 or compressed air tank C GA-320 fitting with a .825-1 4 thread and a petcock valve, a 12" stainless steel braided hose, a patented bleeder valve and a female Foster fitting. This adaptor is made for both CO2 or compressed air. For compressed air charging the Crosman unique bleeder valve is a necessity. To take full advantage of the Discovery rifles this is a must have accessory.