For use in harnesses, you can't do much better (especially for the price) than the Doc Johnson Plated Chrome ring. I have these in several sizes for use with different-sized appendages, and they do a fantastic job. They're easy to change out and fit my toys snugly. Best of all, they're smoothly polished, so as not to damage my toys.

They're also very easy to clean. I run mine under warm water, wash with anti-bacterial soap, and dry with a clean towel. I do recommend you are careful not to scrub them, because the chrome finish is only plating and could potentially chip. I have not yet, however, had this issue.

My partner has not been brave enough to use these as a cock ring yet because he finds the material pretty intimidating. There's also a small gap that seems as though it might have the potential to pinch the skin; however, it doesn't seem to have been a problem for other reviewers here, nor has it happened to any of my toys. If you're interested in a metal cock ring and have never used one before, I suggest doing some research first. They have potential to do serious lasting damage if you're not careful. For someone more experienced with cock rings, however, I recommend them based on the construction alone. They're high quality, non-irritating, and seem like a good investment.

One note, the product description on Edenfantasys seems to imply that you can use this for piercings in some way (not really sure what they mean, to be honest). As a bit of a piercing elitist I have to stress that this not a good idea. These are much too heavy to hang off of most types of piercings, and the material is not suitable for that application. If you're going to do anything regarding these rings and piercings, please be very careful. Again, this is another instance where it's important to do your research.