The invention provides an improved gas cylinder and valve for filling or discharging a gas cylinder comprising a body having a first end, a second end, and an axial bore for providing a passageway for flow of fluid. A collar is provided having an outer surface for engaging an external member to the valve for accepting or discharging fluid. A core is provided having an axial bore for receiving a pin disposed within the body and providing a passageway for flow of the fluid. The first end of the body is adapted to removably mount and rotationally fix the collar. The first end of the body is further adapted to removably receive the core, whereby the core retains the collar on the body when the core is received by the body.