seattlcpl said: I have a huge collection of them in all kinds of materials, steel, titanium, silver, copper, jade, glass, tungsten carbide, leather.
For size you can do what other posters have said and measure with string. You can also go to the hardware store and buy a few different sizes of o-rings and try them out. The silicone o-rings come in a variety of sizes and they are cheap. You can figure out your size from there and then buy a more expensive ring if you want. They also sell cheap metal rings in the rope and tackle section. Sized right, you can wear a ring all day as jewelry.
If you want to experiment first, there’s a leather/rubber ring called a speed strap. It’s got a bunch of snaps on it and you just size it appropriately, and when you want to take it off, just pop the snaps. Easy peasy. Also a good starter way to get into it.
The more advanced rings are called cock cages, and are several rings combined into one. So one around the base (cock and balls), one for the balls, one for the shaft. Some 4 ring cages separate the balls. Some incorporate ball stretchers, or stacks of rings that go around the balls. Lots of fun.
Like you, I use several types. Mostly steel or aluminum, either band type, donut type, or ergonomic (which fit well, work well, and are easy to take off). I started out with the stretchy kind, and once I got used to wearing that I then tried metal O rings from the hardware store, estimating my size by measuring my diameter at the base, and then getting similar diameter rings (50mm). I then went to 45mm inner diameter, which was a little more snug than 50mm. but I could still get a pinky finger between ring and penis, which is a good measure to tell that it's not too tight on you.
I forgot about the leather snap kind. I tried one a few years ago, but it broke. But yeah, it's very safe and a lot of guys seem to use them.
I think any time someone is messing with rings down there they need to take their time getting used to using one, and start out with the safer ones. Know what you're doing. Listen to your body. And if you are using a stiffer material type of ring, TAKE BREAKS. It's just common sense.