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The maker of this device, Ternence, has an entire series of cages that use a hinged ring. Not all of their products pop up on their store page, so you might have to do some digging around.
Edit:they also have a latex tube you can put over the hinge to prevent pinching
I've been wearing this for about 2 months, and I'm loving it. It's comfortable, short, and because of the bend my underwear doesn't rub on it. I can even shower with it, so realistically I only have to take it off once a week or two for deep cleaning.
On the other hand, if we're talking truly invisible, like flirting in a short skirt and panties kind of invisible, you might want something like this. I also have one of these, and it takes a little work to keep clean, but it's pretty comfortable.
Right here! TERNENCE Ergonomic Design... https://www.amazon.com/dp/B07GKWGHHT?ref=ppx_pop_mob_ap_share