Manual Damper, 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, Overall Length 40 in, Frame Depth 1 5/8 in, Rough Opening Length 38 in, Maximum Pressure 1 in wc, Rough Opening Width 33 in, Blade Material Aluminum, Single Acting/Double Acting Single Acting, Closure Type Spring, Flange Width 1 3/8 in