Test objects for compatibility with LEGO(r) Technic axles and '+' shaped axle-holes.There are several holes with slightly different inside dimensions, so you can measure very precisely how your 3D printer handles the critical dimensions.Print these out on your 3D printer. Try inserting '+' shaped axles into the various '+' shaped holes. Some holes will not fit at all and others will be too loose. It depends on the precise details of how your 3D printer deals with inside dimensions of holes. Use the results of your experiment to calibrate SCAD files that you use to create other objects.One has holes aligned with the X axis, the others are rotated to a 20 degree angle; also one has thicker edges all the way around. Depending on your 3D printer, one will be better than the others. Full instructions and further explanation are in the block comment of "xhole-test.scad".For more accurate measurement, you can use the tapered axle test object "axle-test.scad" ( thingiverse.com/thing:40594 )