size 20x20 mm ring
thingiverse
A compact ring is what you're referring to.
Download Model from thingiverse
With this file you will be able to print size 20x20 mm ring with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on size 20x20 mm ring.