If you use screws and bolts on your designs, this device will help you pick the hole sizes to use. The through-holes are for spec’ing holes for bolts or the loose ends of screws. The pegs with holes picking a hole size for sheet metal screws that you want to bite into a part of your model. I made this because holes never come out exactly as you spec them in the model.
Download the model here: Screw hole gauge with OpenSCAD source by rlb408 - Thingiverse