22mm bearing width for body, 7-8 mm height of bearing. Print caps separately for different colour. Try printing it in transparent filament. 

1. Print the caps first to see if it's a good fit for your finger size.
2. Print the body.
3. Push in bearing once printed (It'll be a tough fit) into the body
4. Push in the bearing caps, so that it's aligned equally through the centre in the bearing itself.

The fidget spinner is light, but spins well. Darker colours like blue and green might suit the spinner. Maybe consider transparent filament. It would look awesome with a bearing in the middle of a clear structure.