I needed a plug to close a hole in my yacht deck that cables passed through. This is my general design for a plug of any diameter that has 0 to 3 holes at the edge to allow up to three cables to pass through. Minor gaps can then be sealed with silicone if desired. 

To make the .stl file, open the deckplug.scad in OpenScad and supply the diameter of the hole in the deck. Then supply the sizes of the cables passing through the hole commenting out any holes you do not need. The separation of the holes can be modified by specifying the angle between them. That's all!