Backdraft Damper, Roof Mount, Exhaust, Damper Size (In.) 35 x 35, Overall Size (In.) 37 x 37, Flange Width (In.) 1 in, Max. Velocity (FPM) 2,250, Construction Material Aluminum Blades, G-90 Galvanized Steel Frame, Nylon Bushings and Galvanized Steel Tie Rods., Stainless Steel Pivot Pins, Use w/Dayton Ventilators 4HX88, 4HX99, Includes Pre-punched Conduit Hole Knock-out and Felted Edges For Quiet Operation