I once tried to make perfectly square holes in my Akula GRP hull.
	This proved more difficult than I first thought. I tried square files. If a file is square it must make a square hole – right. Wrong. I have 4 different square files, all have a very slightly rounded edge to them. After a few passes though a drilled hole, the square started to take shape, but the corners were not as crisp as I wanted them. How to fix this? I’ll place fine sand paper around a square brass tube. Wrong again. The corners weren’t as sharp as they should be. As I kept correcting the problem, I noticed that more material was being taken away and my holes began to increase in size. And what happened to the alignment!
The solution: Square Tube Styrene
	Cut a piece a little longer than the thickness of the hull. Place this around a square piece of brass tubing. The Outside Diameter (OD) of the brass square tube is the same as the Inside Diameter (ID) of the square styrene tube. The brass tubing will help in holding the piece and help in aligning the piece in the hole.
	Make the square hole in the hull slightly bigger that the OD of the styrene. Place a drop of CA glue only on one side of the tube, between the styrene tube and the hull. Important: make sure the side that has the glue on it is the side that is square to the alignment of the holes. This will greatly help in the over all alignment of all the holes. Hold or freeze with kicker. Next fill all around with CA glue, on top and underneath. After the glue has dried file and sand smooth.
	Better than freehand. A perfectly square hole and best yet all holes are symmetrical.