Inspired by Numberphile's video on centrifuge problem https://www.youtube.com/watch?v=7DHE8RnsCQ8 In short, this is a visualization tool on how to balance 12 slot centrifuge, especially for the case of 5 and 7 test tubes(in this case nuts).

You will need:

-1x 608 bearing

-12x M8 nuts, with edge to edge diameter of 12.8mm, preferably nyloc

Problem with nuts is their wide tolerances. According to ANSI standard, their edge to edge diameter is 12.73-13mm, that's the difference between falling out and not fitting at all. Either find ones that are close enough to 12.8mm, or you can modify f3d file(use parameters table).