Basically this idea came to me when I wanted to try to make a 3D printed helmet, but needed to be sure its dimensions would fit. You use a large metal yardstick and put one end on where the hole is then the other end slides over the metal yardstick. I printed the hole end standing up without supports and the other part on its long side so that it also does not need supports. Suggest 0.2 mm layer height and 10% infill.