B-Vent Round Pipe Increaser Outer material - .018 Thick, G-90 Galvanized Steel Inner Material - .012 Thick, Aluminum sizes 3" X 4" through 7" X 8" Inner Material - .016 Thick, Aluminum sizes 8" X 10" through 12" X 14" Available Sizes 3" X 4" Through 12" X 14" Diameter