Black Iron Register - Measures Inner Diameter: 10 Inches (254 mm) by 4 Inches (102 mm). Outer Diameter: 12 Inches (305 mm) by 5 1/2 Inches (140 mm). Comes With Louvers. Drop In Style Standard. These are individually cast in solid iron - durable and heavy for decades of service. The cast iron is approximately 0.2 inches thick (5 mm) and will easily hold over 400 pounds.