SH Naiture 4" x 14" Cast Iron Floor Register Antique Style Duct opening size: 4" x 14" (Overall size: 5-3/4" x 15-5/8") Made of 6.45mm heavy cast iron with rustproof black powder coat finish for durability and reliability. Louver control extension from register: 3/8" which could control air flow easily by foot. Steel louvers are painted black for low visibility. To determine size needed, measure air duct opening rather than old register or grille.