5", 5RV-AF, Adjustable Flashing 0 to 6/12, Round Top. Type B Gas Vent. Used where the vent passes through a roof. The RV line of MetalBest round Type B gas vent pipe and fittings is designed for use on approved gas appliances in residential and light commercial and industrial applications. Size refers to the inside diameter of the pipe or fitting. The outside diameter of RV is approximately 1/2" larger. Outer material is 28 GA galvanized steel. Inner liner is aluminum.