Visit http://fidgetexpert.com for more projects and guides. :)
A tri fidget spinner I made in 123D Design. Uses one skateboard bearing together with three hex M8 nuts.
Right from the bat the sockets for the hex nuts are a little bit too small, so use a lighter to heat them up, then push the nuts through for a perfect tight fit. This will ensure they will not fly out of their sockets.
I recommend that you print a cap for the ball bearing as well.