One brand new air compressor 3/8" female NPT pipe thread x 3/8" male NPT thread in tank check valve. The 3/8" male NPT side is usually used to screw into the air tank and the 3/8" female NPT 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 an unloader line, if your compressor does not need the unloader port it can simply be plugged with a 1/8" NPT plug.