Naiture 4" x 10" Cast Iron Floor Register Modern Style Duct opening size: 4" x 10" (5-3/4" x 11-3/4" Overall) Heavy cast-Iron with rustproof black powder coat finish for durability and reliability. Louver control extension from register: 5/8" which could control air flow easily by foot. Includes removable louvers. To determine size needed, measure air duct opening rather than old register or grille.