This is my knurled keychain fidget spinner. It uses a single 608 skate bearing and has either a fine or coarse knurling. I like it because its really easy to fidget with in your pocket.
If you don't have a 3D printer but still want my design, please consider checking out my etsy.
Monoprice Maker Select Plus
I used 0.1 mm since I needed to make out the fine details of the knurling.