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: SilverMaterial: Galvanized IronOuter Diameter of Interface: 147 mm / 5.79 inchOverall Size: 197 x 1 mm / 7.76 x 0.04 inch (L*T)Packing List: 1 x Duct Manual Volume DamperAdvantage1. Made of durable Galvanized Iron, which has high hardness and high temperature resistance, not easy to deform and corrosion, moisture-proof and fade resistant, 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.