I have found a glans ring can be amazing or a nightmare and it all comes down to a few mm
I experimented with many until I finally found for me is a nearly perfect setup.
First trick is sizing matters. As does flexibility. Metal rings were a hard fail several times. My Lori would either not hold me or cut into me because there was no flex and I was a grower. I would shrink so small I would come right out or it would actually cut k to the skin when I was hard too long. All bad.
I then moved to rubber o rings. Lots of options and sizes here. This was a lot better and I was able to find a size that was almost perfect but I still had issues after a while with it cutting into the skin under the head after a few days.
The revelation was in finding that there is very different materials you can get rubber o rings in. Most of them are black nitril. There is not a lot of stretch in them but they are reasonably soft.
The trick was to get white silicone o rings. They have a lot more stretch and I was able to find one that fit me comfortably when he’s small and not fall off but also could stretch a bit when things tightened up.
The last trick is figuring out how to attach the o ring to whatever you are mounting it on. I tried small zip ties and found it would irritate me because of the hard plastic. I tried pony tail bands. Almost everything.
Then I discovered the whole silicone plumbers tape. It’s very thin but strong and does not bother me. I cut a length of it and then tie it to either the bottom bar of my kink3d cage or to my Lori retainer ring mount (I cut off the metal ring).
Could I pull and break the pluming tape or cut it with small scissors? Yes but I would never be able to get back in to reassemble things without the key or it being obvious.
This setup has worked for weeks at a time. The silicone ring is very comfortable and the plumbing tape has lasted for 3-4 weeks of wear so far ( across 2 sessions).
I will swap the tape for a fresh piece next time I am let out (who knows how long!). The silicone ring should pretty much go as long as it’s needed.
Best way to get the size right is to order a kit like this with a bunch of different sizes. Then you can experiment. I would say try without a cage and make sure it stays on you just behind the head for a day or so and does not hurt or cut to much.
Here is a option from Amazon