One ring to rule them all. This model was based on this image, using MATLAB R2016a to make the "height map" of the inscription on a toroid insted of an sphere, like most of the models I've made by this way. The files have different inner diameter, from 16 to 24 mm. All of them are the same file scaled to fit to the inner diameter. It is also included a 9cm diameter ring if you want to use it as a bracelet.
Update: all the models were changed following standard sizes from here. You can check this to find the equivalent for the different size conventions. I recommend to download directly from the files, because all the files together makes a heavy package.
It is recommended to use brim or raft because of its small contact surface with the bed. The details of the inscription are to small for the usual 0.3mm resolution, it is recommended to print it with the resolution as low as possible.