52 In.H-W 4.5 In.L Aluminum Backdraft Damper, Damper Application Backdraft, For Nominal Duct Diameter Not Applicable, Frame Material Galvanized Steel, Number of Panels 1, Maximum Air Velocity 2250 fpm, Overall Height 52 in, Rough Opening Diameter 50 1/2 in, Rough Opening Shape Square, Fits Fan Diameter 48 in, For Duct Shape Square, Free Area 15.4 sq ft, Overall Width 52 in, Frame Material Thickness 20 ga, Overall Length 4 1/2 in, Frame Depth 2 in, Rough Opening Length 49 1/2 in