27.75 In.H-W 4.5 In.L Aluminum Backdraft Dampr, Damper Application Backdraft, For Nominal Duct Diameter Not Applicable, Frame Material Aluminum, Number of Panels 1, Maximum Air Velocity 2250 fpm, Overall Height 27 3/4 in, Rough Opening Diameter 25 1/2 in, Rough Opening Shape Square, Fits Fan Diameter 24 in, For Duct Shape Square, Free Area 3.8 sq ft, Overall Width 27 3/4 in, Frame Material Thickness 0.1 in, Overall Length 4 1/2 in, Connection Type Not Applicable, Frame Depth 1 5/8 in