fidget spinner ring with ISO thread

Inspired by the [Customizable Fidget Spinner Ring](https://www.thingiverse.com/thing:188275), but not happy with the gaps and tolerances as the rings come apart, I had to fire up Fusion and create my own version. Failing in creating the knurling, I chose the ISO thread as spinner.

The inner and outer rings are 0 tolerance, and fit nicely together. For changing the spinner, you can push the rings apart with the nails between the spinner and the edges of the rings.

Attached you will find the US size 8 (18.2mm) ring. For any other size, ping me and i will upload. The edges are chamfered, for a more comfortable wearing.

The dimensions are based on .45mm perimeter extrusion. If you use prusa slic3r, import as individual objects, not one project. optimal layer height .2 for all layers.