This just adapts a 3/8 nut to replace expensive 22mm 608 bearings and can add a little extra color to your toy.
The nut I used measures .678in outside. I just had them laying around and they're nothing special. Enjoy. Feel free to convert to metric or remix however you'd like. A credit would be nice if you remix but I didn't exactly invent an anti-matter engine here.
I didn't know that there was another one of these already on thingiverse, but this is fully my work. I've included the Fusion 360 file for your convenience and possible modification.
Mine spun for about 2min 28 sec to a dead stop (-2 sec to hit the stopwatch and spin it.)
If you print these, please consider taking a picture and/or writing something. We as Makers can't improve if we don't have feedback. Thanks :D