Description This Check Valve has a flow direction of 9/16 UNF Male (with flare) – 3/8 NPT Male Provides maximum resistance to prevent back pressure to your compressor Normally placed between the compressor and air tank, or manifold block The check valve prevents pressure leaking back into the compressor which can cause longer fill times, the possibility of leakage and / or damage to your compressor There are other thread combinations by using our 3/8 Check Valve and Flare Fitting