Model 123 Rev C Back Pressure Regulator, Graphite/NBR Gaskets; 1/2" Line Size; Cast Iron Body With Cast Iron Spring Chamber; B4 Trim: Brass With PTFE Seat, Fluorocarbon Elastomer (FKM) Diaphragm; NPT End Connections; 40-100 PSIG Range Spring; OPT-1: Closing Cap