The Master Flow 12 in. x 6 in. x 6 in. Universal Register Box with Flange is made of galvanized steel. It creates a straight (in-line) transition from round pipe or insulated flexible duct to an air register or grille. The built-in flange helps to create a more secure installation by providing an area for register screws, Sheetrock frame or nails for joists. The flange creates the ability to install the box before dry walling.