Google Knuckles
thingiverse
Index finger holes are slightly larger, at 20mm. If your index finger is bigger, try scaling it proportionally to see if it fits better. For a more comfortable grip, you can bring the G back in a bit. Most edges have a slight bevel.
Download Model from thingiverse
With this file you will be able to print Google Knuckles 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 Google Knuckles.