3/4" MNPT x 3/4" FNPT Air Compressor In Tank Check Valve New 3/4" male NPT by 3/4” female NPT air compressor in tank check valve, with 1/8” female NPT threads on the side for un-loader port. Check valves are used to prevent backflow of air. This style is used to directly screw into the air tank and keep pressure from leaving the tank and putting pressure against the compressor pump once the compressor is shut off. This item is made in the United States by CONRADER CO. Specifications: Air inlet threads: 3/4" female NPT which measure about 1” in diameter Outlet threads: 3/4” male NPT which measure about 1 1/32” in diameter. (These threads are the male threads that screw into the air tank) Side un-loader port: 1/8” female NPT which measure about 5/16” in diameter. (This port is used for a un-loader line. Some compressors do not have this; if yours does not, you would just plug this port.)