This stock replacement fuel valve shuts off automatically when the engine is off. On starting, the vacuum created by the engine activates a diaphragm which opens the valve again. For safety reasons there is an additional conventional lever, too. The installation of this valve requires a vacuum hose fitting on your manifold or carburetor (as used on Harley models from 1981 up) which has to be installed if not present. All those who once found their bike sitting in a big puddle of fuel (no smoking please) just because of a grain of sand in the float needle valve will appreciate the additional safety of this device. With a 22 mm adapter nut the petcock will fit all OEM  tanks 1975-up and all aftermarket tanks that feature the same type of outlet.