35.75 In.H-W 4.5 In.L Aluminum Backdraft Dampr, Damper Application Backdraft, For Nominal Duct Diameter 36 in, Frame Material Galvanized Steel, Number of Panels 1, Maximum Air Velocity 2250 fpm, Overall Height 35 3/4 in, Rough Opening Diameter 36 in, Rough Opening Shape Square, Fits Fan Diameter 36 in, For Duct Shape Square, Free Area 8.2 sq ft, Overall Width 35 3/4 in, Frame Material Thickness 20 ga, Overall Length 4 1/2 in, Frame Depth 2 in, Rough Opening Length 36 in, Maximum Pressure 1 in wc