On a ship, the function of an airport or porthole, when open, is to permit light and fresh air to enter the dark and often damp below-deck quarters of the vessel. The Cast Your Anchor airports are composed of machined brass rims that have a flange and ring for easy and secure insertion into pre-bored holes. The airports have the added feature of concealing any raggedness around the perimeter of the hole. Inside, there is a machined seat for acetate, or cover glass "glazing". Most airports come with an acetate insert or you can use brush on glaze for a more realistic look.