Naiture 4" x 12" Cast Iron Floor Register Geometric Style Duct opening size: 4" x 12" (5-1/2" x 13-3/4" Overall) Made of heavy cast-Iron with rustproof black powder coat finish for durability and reliability. Louver control extension from register: 1/2" which could control air flow easily by foot. Installation type: floor To determine size needed, measure air duct opening rather than old register or grille.