Newton fuel tank roll over valve -8JIC (3/4"UNF) thread to fit to tank; -6JIC threaded union for vent to air. A fuel tank valve that allows; 1) air to replace fuel used. 2) air to escape due to heat expansion. 3) a positive shut off to prevent fuel escape due to splashing or roll over. This is achieved by a two ball system one. Valve must be mounted vertically.