33 In.H-W 5 3/4 In.L Alu Wall Backdraft Damper Damper Application Backdraft For Nominal Duct Diameter Not Applicable Frame Material Galvanized Steel Number of Panels 1 Maximum Air Velocity 2500 fpm Overall Height 33 in Rough Opening Diameter 30 1/2 in Rough Opening Shape Square Fits Fan Diameter 30 in For Duct Shape Not Applicable Free Area 5.5 sq ft Overall Width 33 in Frame Material Thickness 20 ga Overall Length 5 3/4 in Connection Type Not Applicable Frame Depth 2 1/2 in