21mm
thingiverse
Personalized rendition of http://www.thingiverse.com/thing:44815, designed using the Customizer at http://www.thingiverse.com/apps/customizer/run?thing_id=44815. For customization, set cursor to 100, groove depth to .3, enable edges with a margin of 0.1. Select type 1 and weight 11 while setting the diameter at 21. Increase surface detail with $fn = 50.
Download Model from thingiverse
With this file you will be able to print 21mm 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 21mm.