Round Zoning Dampers are made of steel for long lasting durability. Built for installation flexibility, reliability and reduced callbacks. Enhanced design provides longer and quieter operation over life span of damper. Gasket ensures low leakage, reinforced blade construction, mechanical visual position indicators and use same universal motor as rectangular ZD damper. RRD Round Dampers easily inserted into rigid round ducts for retrofit zoning in forced air heating and cooling systems. Length is 6". Motor type is Power Closed, Spring Open, Reversible. Mount type is Side.