A little necklace thing to hold your rings if you need to take them off, but want to carry them with you. Could be useful for people who wear protective gloves at work.

Printing

Printing should be easy, this one was made with a 0.25mm nozzle, but 0.4mm should work too. Resize the model to fit your ring. I've included the .blend file (enable Bool Tool addon) for easier edits. Infill and extra perimeters won't matter much, as low as 

Since it's sort of a necklace, maybe pick a nice color filament that goes with your clothing. I'd use PLA, as it usually has a nice surface finish.

Assembly

You will need a piece of string. The string goes through both holes and ties behind your neck.

How to use

I've included a video to clarify, because string topology is weird. 

You just push the ring in from one side, turn it around the bottom, pull it up the other side, and let go. To get it out, same thing, in reverse if you prefer, but it won't matter, works both ways.