Selkirk 104825 Type"B" Gas Vent 4-Inch Adjustable Flashing 0 to 6/12 Pitch
4", 4RV-AF, Adjustable, Flashing 0 to 6/12, Round, Type B, Gas Vent. Used where the vent passes through a roof. Outer material is 28 GA galvanized steel. Inner liner is aluminum.