In some recent projects I utilized some precision bolts as axis for ball bearings. Due to the tight fitting they are really cumbersome to get in by hand, that's why I created this little helper to push them in by force with a regular M5 screw and nut.
It is designed for 625 ball bearings with 16 mm outer and 5 mm inner diameter. Usage should be self-explanatory from the picture above. Works like a charm!
I added a parametric OpenSCAD version that let's you design your own piece. Please note I have not printed the generated part yet, measured dimensions look OK though.