I loved Zigians "The Last Spinner Cap", it fits perfectly and grabs the bearing really well - however, I prefer my caps to have a concave cup to hold your finger/thump in place. I took his 22mm wide "tall" cap, and added a small outside ridge and inner concave to it and it's now my perfect Finger Spin cap.
Updated : I made an even better model, slightly taller which gives more of a cup for your finger to sit in. Both caps work great so it's personal preference.
Monoprice Maker Select Plus
If you print higher than 0.2mm layer thickness the concave won't be quite right.