I designed this just for fun but they actually work quite well also. I was interested in seeing how to print two components together without them bonding. I used a 0.2mm print layer and a 0.2mm gap between the two rings. They stick together but don't fuse together and can be pried apart quite easily.

The rings are 20mm, 30mm, 40mm and 50mm inside diameter. The smaller rings are definitely stronger but all are useable. I printed them all as one set and it worked well. But I am including individual rings in case you don't want them all. Take note of the print settings though, they will be particularly important if printing one ring at a time.

Note the print settings below.

Many more of my designs are posted at... https://logicalplanet.com