I got the idea for this from the Reverse Engineer's Ring. To quote that thing's description:

Sans professional rite of passage, the Reverse Engineer's Ring is a variation of a Canadian engineering tradition - the Iron Ring.

The Reverse Engineer's Ring is to serve as a reminder that you don't have to be building bridges or parking structures to have the potential to accidentally ruin somebody's day or somebody's life with your creations. Out of respect for the original tradition, the design of the ring is coarser in appearance (six facets top and bottom instead of twelve). The ring should be worn on the little finger of your dominant hand, such that when you draw or write, the flat edges rub against the page.

I used the wonderful Nut Job with the measurements I wanted, lobotomized the thread cutting bit of code, and simplified/edited it in Blender to finalize it.

The measurements are 20 mm inside, 25 mm outside (flat to flat), and 7 mm high.