Model 31-B Rev A Low Back Pressure Regulator; 3/4" Line Size, #6 (0.375") Orifice; Stainless Steel Body And Lower Case, Carbon Steel Spring Chamber, Actuator Mounting Position 4; S40N Trim: 316L Stainless Steel Internals, BUNA-N (NBR) Seat And Diaphragm, Nylon Loading Ring; NPT End Connections; 3.0-4.5" wc Range Spring; Internal Sensing