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39 In.H-W 6.5 In.L Fiberglass Backdraft Damper, Damper Application Backdraft, For Nominal Duct Diameter Not Applicable, Frame Material Fiberglass, Number of Panels 1, Maximum Air Velocity 2500 fpm, Overall Height 39 in, Rough Opening Diameter 36 1/2 in, Rough Opening Shape Square, Fits Fan Diameter 36 in, For Duct Shape Not Applicable, Free Area 7.4 sq ft, Overall Width 39 in, Frame Material Thickness 0.1 in, Overall Length 6 1/2 in, Connection Type Not Applicable, Frame Depth 3 in