57 In.H-W 5.75 In.L Aluminum Backdraft Damper Damper Application Backdraft For Nominal Duct Diameter Not Applicable Frame Material Aluminum Number of Panels 2 Maximum Air Velocity 2500 fpm Overall Height 57 in Rough Opening Diameter 54 1/2 in Rough Opening Shape Square Fits Fan Diameter 54 in For Duct Shape Not Applicable Free Area 16.7 sq ft Overall Width 57 in Frame Material Thickness 20 ga Overall Length 5 3/4 in Connection Type Not Applicable Frame Depth 2 1/4 in