spring (6.2mm inner, 9mm outer, 10mm height, with rings at top and bottom)

thingiverse

I made a remix that's smaller and has a top and bottom ring. Print it very slowly (I printed at 1500mm/sec) and quite coolly (I did 185 instead of my usual 195-200 for PLA), or else you won't build in height, it will just sag. Also, make sure the layers are as thin as possible, or else the overhangs will be bigger the thicker the layer is. I used .15mm and that was too much - go as small as your printer allows for something this size. It should scale up well, probably not down though, it's already quite tiny. Good luck with it.