This cast brass porthole window has a 9 inch frame. The original glass is 5 inches in diameter. The opening window frame is 6 1/2 inches wide and opens and closes a bit tight. The wing nut closure on this cast brass porthole window also moves a bit tight to lock the window closed. The flange ring on the back measures 6 1/4 inches in diameter and extends back from the main frame by 2 inches. This porthole weighs nearly 7 pounds.