Hole and pocket calibration shapes.

thingiverse

Holes and pockets are sized to 3, 5, 8, 10, 12 and 15mm. Print it out, check your actual sizes and now you know how much to under/oversize holes in your designs :) You should be done calibrating your printer before you figure out hole sizing like this. Its particularly reliant on the extrusion flowrate and settings that relate to that like filament diameter. Made using FreeCAD, FreeCAD file is also included.