32.75 In.H-W Alu Universal Backdraft Dampr, Frame Material Aluminum, Number of Panels 1, Maximum Air Velocity 2250 fpm, Overall Height 32 3/4 in, Rough Opening Shape Square, Fits Fan Diameter 30 in, Free Area 4.8 sq ft, Overall Width 32 3/4 in, Frame Material Thickness 0.1 ga, Frame Depth 1 5/8 in, Rough Opening Length 31 in, Maximum Pressure 1 in wc, Rough Opening Width 31 in, Blade Material Aluminum, Single Acting/Double Acting Single Acting, Closure Type Spring, Flange Width 1 3/8 in