54 In.H-W 5.75 In.L Aluminum Wall Shutter Damper Application Backdraft For Nominal Duct Diameter Not Applicable Frame Material Aluminum Number of Panels 2 Maximum Air Velocity 2500 fpm Overall Height 54 in Rough Opening Diameter 51 1/2 in Rough Opening Shape Square Fits Fan Diameter 48 in For Duct Shape Not Applicable Free Area 14.8 sq ft Overall Width 54 in Frame Material Thickness 0.8 in Overall Length 5 3/4 in Connection Type Not Applicable Frame Depth 2 1/2 in