Naiture 4" x 10" Cast Iron Floor Register Old Victorian Style Duct opening size: 4" x 10" (Overall size: 5-1/4" x 11-1/8") Heavy cast-Iron with rustproof black finish for durability and reliability. Louver control extends 3/4" H from vent which could control air flow easily by foot. Removable louvers. To determine size needed, measure air duct opening rather than old register or grille.