This 12 inch galvanized copper finish porthole measures 12 1/2 inches in diameter and is made of iron. The original glass measures 7 7/8 inches in diameter. The opening window frame is 9 inches in diameter and opens and closes freely. The wing nut closure moves freely to lock the window closed. The flange ring on the back of the frame is 8 1/4 inches in diameter and extends back from the mounting ring by 1/2 inch. This porthole weighs almost 10 pounds.