Backdraft Exhaust Damper No-flange Horizontal or Vertical Mount Damper Size 39 3/4 X 39 3/4 In Overall Size 39 3/4 X 39 3/4 In Outside Flange 39 3/4 X 39 3/4 In. Max Velocity 2000 FPM Construction Material G-90 Galvanized Steel Frame and Aluminum Blades Includes Pre-punched Conduit Hole Knock-out and Felted Edges For Quiet Operation