The Master Flow 10 in. duct-board Starting Collar is suitable for 1 in. to 1-1/2 in. duct-board plenums. It provides a transition from the plenum to round pipe or insulated flexible duct. This starting collar has a built-in damper which allows for adjusting air flow within the duct run. It can be used with duct-board, an internally lined or unlined plenum. This galvanized steel starting collar features extra-long tabs.