Duct Start/Take Off Collar, Boot Style Speedi-Boot Hanger, Collar Diameter 4 1/8 in, Collar Connection Height 4 1/8 in, Collar Connection Width 9 3/8 in, Material Plastic, Compatible Register Height 9 3/8 in, Compatible Register Width 9 3/8 in, Duct Size 8 in, Cap/Collar Material Plastic, Product Type Register Boot, Damper Type Manual, Standards UL 2043 Classified