Naiture 4" x 12" Solid Brass Floor Register Modern Style Oil Rubbed Bronze Finish Duct opening size: 4" x 12" (Overall size: 5-1/2" x 13-1/2") Made of heavy-duty solid cast brass for durability. Finished with a durable oil rubbed bronze powder coat finish to resist rust. Louver control extension from register: 5/8" which could control air flow easily by foot. To determine size needed, measure air duct opening rather than old register or grille.