3/8" Male NPT x 3/8" Compression Check Valve CTLD3838T Air compressor 3/8" male NPT pipe thread x 3/8" Compression thread in-tank check valve. The 3/8" male NPT side is usually used to screw into the air tank and the 3/8" 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 an unloader line, if your compressor does not need the unloader port it can simply be plugged with a 1/8" NPT plug. Specifications: Made in the USA Total Length Of The Valve: 2-5/16" Male Pipe Thread Size Used To Screw Into Air Tank: 3/8" Male NPT Compressor Line Input Threads: 3/8" Compression Thread Unloader Line Input Threads: 1/8" Female NPT