I needed a boom to mast plate that could accomodate both the 1" boom of a UHF yagi, and the 2" diameter of a mast. Array Solutions sells one, but it didn't go up to 2" and was kind of expensive for what it was, so I decided to make one myself.
I could've laid out the drill pattern by hand on a piece of
aluminum, but figured I would want to make more at some future
date. So I laid out the pattern instead in a graphics
program. By printing it out on paper and gluing it to the
material it is trivial then to use it as a drill template with very
good accuracy. I have made a number of these now and they work