We are offering 800 usf socket 1. Time tested and proven for over 30 years to be precision perfect and leakage free. Helps build efficient air lines everywhere onboard with an uncompromising standard of quality and flow performance in each and every application. The plug and socket fitting portion of couplings 20, 30 and 40 are interchangeable, as are those of the 400, 600 and 800 couplings. This means that a coupling 20 may be connected to a 30 or 40, the only difference being the flow capacity of the couplings. Bsp thread.