42 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 1 Maximum Air Velocity 2500 fpm Overall Height 42 in Rough Opening Diameter 39 1/2 in Rough Opening Shape Square Fits Fan Diameter 36 in For Duct Shape Not Applicable Free Area 8.5 sq ft Overall Width 42 in Frame Material Thickness 0.8 in Overall Length 5 3/4 in Connection Type Not Applicable Frame Depth 2 1/2 in