35 In.H-W Alu Universal Backdraft Dampr, Frame Material Aluminum, Number of Panels 1, Maximum Air Velocity 2250 fpm, Overall Height 35 in, Rough Opening Shape Rectangular, Fits Fan Diameter 36 in, Free Area 8.1 sq ft, Overall Width 35 in, Frame Material Thickness 0.1 ga, Frame Depth 1 5/8 in, Rough Opening Length 33 in, Maximum Pressure 1 in wc, Rough Opening Width 38 in, Blade Material Aluminum, Single Acting/Double Acting Single Acting, Closure Type Spring, Flange Width 1 3/8 in