The AG-4 Air Gap Fitting is used for indoor installations of all 3/4'''' - 1'''' Model 975XL/975XL2 Reduced Pressure Principle Backflow Preventers for the connection of a drain pipe to the backflow preventer, directing nuisance water discharge to a safe drain. It has iron inlet and 1'''' NPT outlet connections. The AG Air Gap Fitting can be mounted to the body of any drain line made of any standard piping material. The AG prevents a cross connection between the drain and potable water supply. Materials include an epoxy-painted cast grey iron elbow and zinc-plated steel bolts for long-lasting effectiveness.