Check the listing for details. 2Pcs 3" HVAC Duct Manual Volume Damper Airflow Backdraft Damper Control Beige. Condition: New. Listed at 22.47 USD. The manual volume damper is used for air volume regulation in an air ventilation system, widely used in HVAC industry. With that installed in your HVAC systems, you can easily control the air flow rate or close off an air duct if needed, to some extent, it will increase the energy efficiency of your system.SpecificationColor: BeigeMaterial: PPInner Diameter of Interface: 75 mm / 3 InchOverall Size: 130 x 4.5 mm / 5.12 x 0.18 inch (L*T)Packing List: 2 x Duct Manual Volume DamperAdvantage1. Made of thick PP Plastic, which has good hardness, durable, not easy to deform and corrosion, moisture proof and fade resistant, and can be used for a long time.2. The side is designed with a rotary handle, which can adjust the air volume from multiple angles and is easy to operate;3. With a smooth and flat interior design, can ventilate rapidly.