Quick Tri Spinner for Valentine's Day. 608 bearing and 3/8" steel balls. I haven't tested the fitment on the steel balls as I don't have any. If someone prints this out, let me know how they fit. I hope to pick some up soon to test.
Edit: Tested the original design and the balls were very tight. I uploaded a new model that also has rounded edges and the tolerance on the balls should be a little looser. Enjoy!