Up on request a friend of mine wanted a holder for his carpenter pencils as they fall down the deep folding rule pocket when they are getting short. Velux, a window brand, provides a clever solution as a promotional gift (like this: https://i.ebayimg.com/images/g/63AAAOSw~NBdJb8s/s-l400.jpg) but they do not sell it. So I decided to research and do my own.
It fits the square pencils, 12x8mm, the 4x4mm holes can be used to press-fit neodymium magnet. The hole at the top is useful if the pencil gets too short and you have to push out the rest of the pencil with e.g. a nail.
Use the test file to test the fit of the hole, perhaps you need to shrink down or enlarge the model for a perfect fit.