4, IAPMO. Backflow Preventer,1 in,FNPT Pressure 175 psi, Width 4 1/16 in, Length 11 3/16 in, Height 7 7/16 in, Features Allows for Easy Repair and Winterization, Patented Removable Pressure Vessel, Standards Approved by the Foundation for Cross Connection Control and Hydraulic Research at the University of Southern California, ASSE 1013, AWWA C511, CSA B64.