Model 123 Rev C Back Pressure Regulator, Graphite/NBR Gaskets; 1/2" Line Size; Stainless Steel Body With Stainless Steel Spring Chamber; S1 Trim: 316 Stainless Steel With Metal Seat, 302 Stainless Steel Diaphragm; NPT End Connections; 40-100 PSIG Range Spring; OPT-56: Cleaned For Non-Oxygen Service Per Cashco Specification S-1542