59.5 In.H-W 4.5 In.L Aluminum Backdraft Damper Damper Application Backdraft For Nominal Duct Diameter 60 in Frame Material Galvanized Steel Number of Panels 2 Maximum Air Velocity 2000 fpm Overall Height 59 1/2 in Rough Opening Diameter 60 in Rough Opening Shape Square Fits Fan Diameter 60 in For Duct Shape Square Free Area 21.9 sq ft Overall Width 59 1/2 in Frame Material Thickness 20 ga Overall Length 4 1/2 in Frame Depth 2 in Rough Opening Length 60 in