Naiture 4" x 8" Solid Brass Floor Register Antique Style In Oil Rubbed Bronze Finish Duct opening size: 4" x 8" (Overall size: 5-3/4" x 9-3/8") Made of heavy-duty solid cast brass for durability. Finished with a durable oil rubbed bronze powder coat finish to resist rust. Louver control extends 3/4" H from vent which could control air flow easily by foot. To determine size needed, measure air duct opening rather than old register or grille.