One brand new air compressor 3/8" male NPT pipe thread x 1/2" Compression thread in tank check valve. The 3/8" male NPT side is usually used to screw into the air tank and the 1/2" compression side is the inlet for the incoming air coming from the compressor pump. This Valve is also equipped with a 1/8" female NPT threaded port on the side for a unloader line, if your compressor does not need the unloader port it can simply be plugged with a 1/8" NPT pipe plug.