Your fingers never stand still do they? Mine neither... So I created this miniature spinner using one 607 ball bearing. The other ball bearings are just for kicks and to add weight.
This thing spins forever. From start to standstill it takes at least 90 seconds - not bad!
You need one 607 ball bearing. I recommend a ceramics bearing since this things spin forever (C607). The other three bearings are just to add weight. These can be normal 607 bearings. The "ZZ" variant looks nicer since it has fully enclosed sides.
No special slicing instructions. You could slice at 0.2mm layer height and 30% infill. I went with 0.1mm layer height and concentric infill (latest Cura). For the dual version I changed the "dual overlap to 0.2mm".