ALDES 4 Inch Round Spring Loaded Backdraft Damper - Professional Grade Highest Rated Premium Airflow Control Backdraft Dampers Spring-loaded butterfly aluminum damper blades encased in a 20-guage galvanized steel housing May be installed in any position or orientation to prevent backflow and designed for use in AC, Heating, Vent and other HVAC application temperatures from -22 to 180 degrees F (Fahrenheit) Extremely easy and secure inline duct insertion installation. Available in 4", 5", 6", 7", 8", 10", 12", 14" and 16". Minimal pressure to open. 0.04 to 0.08 in. w.g. Maximum automatic back flow protection Designed to be inserted in 4&#034; duct. 20-gauge galvanized steel housing. Aluminum spring-loaded butterfly damper blades. Damper seals against a heavy-duty Neoprene rubber gasket in closed position for minimal leakage. Gasket designed for use in temperatures from -22F to180F. Requires airflows of 0.04 to 0.08 in. w.g. to begin to open. May be installed in any position. The entire assembly inserts into duct for simple installation. Exterior foam gaskets provide a tight seal against interior surface of duct.