NOTE: holes for magnets are internal so you won't see them in the Thingiview. The holes for two 6 x 3 mm magnets are 0.6mm from bottom layer, and extend to 3.6mm. So for printing at 0.200mm layers, you would stop the printer at layer 18 (I used the color change option in Slic3r Prusa Edition) and drop in the magnets, then continue printing to seal them in. If you want you can put a small drop of super glue in each hole to keep it from rattling (don't get it on print bed!). The holes are 6.2 x 3.2 mm to hopefully account for tolerances.