Backdraft Damper / Wall Shutter, Fits Fan Dia. 48 in, Shutter Overall Size 51 in x 51 in, Shutter Construction Material G-90 Galvanized Steel Frame and Tie Rods, Shutter Opening Required 48-1/2 in x 48-1/2 in, Shutter Free Area 12.924 sq ft, Vertical Shutter Mounting Position, Shutter Mounting Location Wall, Frame Depth 3 in, Open Depth 6 1/4 in, Flange Width 1 1/2 in, Mounting Hole Size Prepunched, Max. Velocity 2500 FPM, Blade Material Mill Finish Aluminum