The purpose of this thing is to enable someone with a table-drill (be it a metal one or something like a Dremel on a stand) to drill holes along a circular curve,
without having to adjust the x/y coordinates after every hole.
Instead, you only need to drill a 5mm hole in the center-point of the circle (I actually drill 4.5mm and then hone it to 5mm), stick it on the 5mm parallel pin on the PCB drilling aide, and position the drill above one of the holes.
Drill the first one, turn the PCB until the next hole lines up with the drill, drill the next one and so on.
If the Hole in the PCB is honed to 5H7 it fits tightly on the pin (precision-ground parallel pin with dia. 5m6, 15mm long), there's no danger of misalignment, provided you hit the exact center.
I also used it to mill out half of the center-piece of the board on the picture. The milling bit broke after that (was turning it too fast), so I had to perforate the rest with a drill and break it out.
The mounting holes are meant for 10mm countersunk screws, which fit on my mill's cross-slide. If you have smaller screws, you can either print your own adapter pieces or ask me to make a basic version without holes in a commonly accepted format availlable. Just write me.
I think this thing is particularly useful for (LED-)lighting-related projects. I have developed for an IR-Beacon project I am currently working on. If you find other use for it, please let me know.
!! YOU SHOULD HOLD ON TO THE PCB AT ALL TIMES. Use this device at your own risk !!