Model "BQ" Back Pressure Relief Regulator,Tfe Gaskets (Opt-45); 1/2" Inlets,1/2" Outlet; Bronze Body & Spring Chamber; B4 Trim: Brass With Tfe Seat,Fluorocarbon Elastomer (Fkm) Diaphragm; Npt Screwed; 20-75 PSIG Range Spring; Opt-55: Cleaned For Oxygen Service Per Spec #S-1134