Galvanized Sheet Metal Round volume dampers have manual quadrant adjustment handle. The ideal use is in branch duct lines for adjusting supply or return air volume. They are field installed into sheet metal starting collars or register boots. Can be used for Remodeling, Do it yourself and New Residential projects. These round duct volume dampers slide into ducting & have a manual handle that screws on. Used for air flow control and routing. Duct dampers prevent reverse air leakage in your metal duct lines. These dampers are made from high quality steel and are designed for vertical or horizontal mounting. The damper blades are lightweight yet sturdy for easy opening and closing. They can be used for bathroom fans, kitchen vents and a wide range of hvac uses.