This expands the width of the thumbstick cap on your Logitech G13 macropad.
The thumbstick provided, while grippy, is woefully undersized. It makes using it constantly very uncomfortable.
This ring is curved and convex to the feel of a more modern joystick, and still leaves access to the rubber G13 cap for grip. It pops on and off easily (so as not to damage the rubber cap) while still gripping the original stick firmly.
To attach the ring, simply press it into place until it pops on to the original stick. To remove it, wedge a flathead screwdriver in to the gap and turn to release the grip of the ring while lifting up.

Update 1: I was informed by a user that, if your G13 is older and the thumbstick is not as strong as it once was, that the original design of this may damage the thumbstick on the device. I have updated the design to account for this potential issue.

Update 2: For most printers (my own included) you will have to do some post-print work to ensure that the ridgess reach their full grippy potential. A little xacto work and some sanding should remove any leftover material from the small channels. I tried to design this away, but I was unable to do so without reducing the traction your thumb achieves with the stick.