MODEL "BQ" BACK PRESSURE RELIEF REGULATOR,TFE GASKETS (OPT-45) 1/2" INLETS,1/2" OUTLET; BRONZE BODY & SPRING CHAMBER; B5 TRIM: BRASS WITH TFE SEAT,PHOS.BRONZE DIAPHRAGM; NPT SCREWED; 10-25 PSIG RANGE SPRING; OPT-55: CLEANED FOR OXYGEN SERVICE PER SPEC #S-1134;