At the request of a coworker I remixed the tri-spinner into a single knurled ring.

He wants it without a bearing, since it fits nicely over a finger and it calms him down to put two of these on his index finger so he can rotate them with the thumb.

I kept the size, so it will fit a bearing too, in case someone wants a single-bearing knurled spinner (I think I'll make one for myself hehe).

Fits regular 608 bearings.
I recommend ceramic ball bearings, they spin very well.

Doesn't Matter

No

I just tore apart the original OpenSCAD script until there was only the knurled ring left :-)