I finally tried out my 0.2mm nozzle and made a fidget ring for it. This one is all-day wearable just like a normal ring - at least I found it to be; it does have quite some thickness, and you might find that still comfortable or not. If everything turns out fine, this is a great fidget toy!
Also see my other fidget rings (including a bracelet).

Important: This is a delicate print

• Bed adhesion is really important. Those small gears have very low contact area to the build plate; if one comes off, the print is ruined.
• If a rogue blob of filament accidentally finds it's way into the gears, the print might be ruined.
• I had a failure rate of about 1 in 10.
• Printer settings and filament are critical.
• This model is subject to wear. Continuous use smooths the teeth out, the clearance grows and the gears can shift. I encountered this (using PLA) after about a week of frequent use. I haven't tried other filaments.

Printing:

Choose the right size (I suggest testing that with the ring size set). If you need a size in between two sizes, choose the lower and scale it up by 2-3%. If you are going for multicolor, print a single color one first to check if it works.

• 0.2mm nozzle, maybe 0.25mm is fine, too, I haven't tested that.
• random seams  to avoid bunched seam blobs
• slicing gap closing radius: 0.01mm, since this ring has a clearance of 0.065mm
• wall generator: classic, since Arachne made the rings turn less smoothly in my tests
• external perimeter/outer wall first
• I also disabled only one wall for top layer, I found that nicer.

Slightly pinch the finished ring from various sides so that many small gears break free. Then carefully try to turn the ring. It then needs a few minutes of breaking in.

I used a Bambu A1 mini, a smooth build plate, and Bambu basic and matte PLA. I printed a bunch (wich took quite a while), so if one wears out, I have another one. Also with Bambu-style multicolor systems the wasted-filament-per-ring-ratio goes down if you print them in bunches.

I hope someone prints it with a 0.25mm nozzle on a Prusa and shares their result. When I get myself a Core One, I'll also get such a nozzle.