Only used in the version of valves with the integrated anti vacuum (AV) valve. Includes the 1/8" M BSP threaded cap (now made of PEEK), pin, o-ring and copper gasket. Assembly required. The o-ring slides on to the pin at the bottom where there's a slight slot for it, then the pin is inserted in to the cap, and the cap threads in to the valve, the assembly being sealed to the valve with the copper gasket.