I like the original Ring-A-Thing except for it's chunkiness and completely separate pin. I decided to save a little plastic and revised the design slightly to eliminate the chunkyness, save some plastic and make it a little more "delicate" for small hands.
I wish OpenScad had a filet feature.
UPDATE I added a second scad file and stl. This one has a shorter peg for less plastic and less bulky charms...unfortunately the charms are incompatible with the original Pin based Ring-A-Thing. I'll upload a negative pin hole stl later for this version. I've put this one together at the request of my son. and I didn't want a lightning bolt sitting on a huge pillar of plastic.