Gas Vent Pipe Increaser; Type Double Wall, Round; Applicable Standard UL 441, CUL, NFPA 54/211; Larger End Size 8" Diameter; Smaller End Size 4" Diameter; Material Thickness 0.012" Inner Wall, 0.018" Outer Wall; Material Aluminum Alloy Inner Wall, G90 Galvanized Steel Outer Wall; Used On Gas Vent; Height 8.5"; Warranty 1 Year Limited