27 In.H-W 6 In.L Aluminum Wall Backdraft Dampr, Damper Application Backdraft, For Nominal Duct Diameter Not Applicable, Frame Material Galvanized Steel, Number of Panels 1, Maximum Air Velocity 2000 fpm, Overall Height 27 in, Rough Opening Diameter 24 1/2 in, Rough Opening Shape Square, Fits Fan Diameter 24 in, For Duct Shape Not Applicable, Free Area 3.3 sq ft, Overall Width 27 in, Frame Material Thickness 20 ga, Overall Length 6 in, Connection Type Not Applicable, Frame Depth 2 1/4 in