They can be really great, but you should not order it too tight, or wear it for any extended period of time, such as overnight. They are available in different inside diameters and also different band widths. They can be worn if you have piercings, but no piercing is really necessary.

The size is the inside diameter that you need. The cock ring should be slid on over the penis shaft and over the testicles (one at a time) when you are Not erect. It should be easy to put on when you are soft, then when you do get aroused you should fill it up nicely. A ring is the perfect size when it is loose but stays in place when the penis is soft, but snug when the penis is hard. Naturally lubricants that are safe for the genital area can be used with this piece.

Now if you are looking for a Glans Ring we have those also;
Gold Glans Ring

Steel Glans Ring with Pressure Ball

2 sizes are available either 5 mm or 10 mm. The 5 mm height is 5 mm wide and the 10 mm height is 10 mm wide.