Sheet Metal Gas Vent Pipe; Type Double Wall, Adjustable Length; Size 8 Inch Inner Diameter x 9-1/8 Inch Outer Diameter; Length 18 Inch; Material Thickness 0.016 Inch (Inner Wall), 0.018 Inch (Outer Wall); Material Aluminum (Inner Wall), Galvanized Steel (Outer Wall); Temperature Rating 400 Deg F; Insulation Supplied Yes; Applicable Standard UL 441; Minimum Overlap Size 1-1/2 Inch