Crosman Discovery DUEL FUEL&reg; Fill Adapter, HP Bleeder for high pressure air bottles and CO2 tanks. This adapter is made for both CO2 or compressed air. CO2 or compressed air tank C GA-320 fitting with a .825-1 4 thread and a petcock valve 12" stainless steel braided hose, a patented bleeder valve and a female Foster fitting 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.