Fits 1-1/4 inch 009, 1-1/2 inch 009, 2 inch 009, 2-1/2 inch 009, 3 inch 009, 1-1/4 inch 909, 1-1/2 inch 909, 2 inch 909, 2-1/2 inch 909 3 inch 909, 1-1/4 inch 009M1, 1-1/2 inch 009M1, 2 inch 009M1, and 2 inch 009M2 This air gap for reduced pressure zone assembly, provide an unobstructed, physical separation between the discharge end of a potable water supply line and an open receiving vessel. The installation of an air gap and drain line are recommended on reduced pressure zone assemblies. It can be installed vertically or horizontally (vent elbow required for vertical installation).