Backdraft Damper / Wall Shutter, Fits Fan Dia. 20 in, Shutter Overall Size 23 in x 23 in, Shutter Construction Material G-90 Galvanized Steel Frame and Tie Rods, Shutter Opening Required 20-1/2 in x 20-1/2 in, Shutter Free Area 2.281 sq ft, Vertical Shutter Mounting Position, Shutter Mounting Location Wall, Frame Depth 2 1/2 in, Open Depth 5 3/4 in, Flange Width 1 1/2 in, Mounting Hole Size Prepunched, Max. Velocity 2500 FPM, Blade Material Mill Finish Aluminum. This item has been restricted from sale in the following state (s): []