Air Pressure Regulator & Filter Combo compressor 3/4" & free gauge 3/4" Air Compressor Regulator & Filter Combo w/ Gauge his regulator and filter combo which has a max pressure of 250 psi and will regulate your air pressu There is 3/4" female npt threads on each side for your main compressor line coming in and going out 1/4" female thread on the outer side for your gauge as shown in the pictures. Inlet and Outlet size: 3/4" female npt which measures about 1" in diameter