DP overflow ventilation grille ensures proper air circulation between rooms and premises. The device is mounted into interior doors. It’s especially helpful in case of having solid, floor-to-ceiling doors. The minimum thickness of the door panel for mounting is 25 mm (for 4409DP) and 33 mm for 4513 DP. Supplied as a set of two pcs, inserted into the door on both sides and jointed together with special slots. Further fixed with screws or glue.