Backdraft Damper, Roof Mount, Exhaust, Damper Size 35 x 35 In, Overall Size 37 x 37 In, Flange Width 1 In, Max Velocity 2250 FPM, Construction Material G-90 Galvanized Steel Frame, Aluminum Blades, Stainless Steel Pivot Pins, Nylon Bushings and Galvanized Steel Tie Rods., Includes Pre-punched Conduit Hole Knock-out and Felted Edges For Quiet Operation RestrictionsWARNING: Not for use with kitchen exhaust applications. Roof-MountG-90 galvanized steel frame, 2" deep with 1" flange. Aluminum louvers, stainless steel pivot pins, nylon bushings, and felted edge. Prepunched conduit hole knockout.Backdraft DampersFor belt-drive centrifugal roof and wall ventilators. Max. velocity: 2000 fpm for models up to 19" and no-flange, 2250 fpm for 23" and larger.