Are you looking at the maximum stretched diameter? It would truly help us if we knew what size he is, I agree that a lot of them have the same unstretched diameter but different materials stretch more than others. Sizing is also very important for safety along with comfort. Look through my work shop, lots of information about different kinds of rings, where/how to ware them and how to measure to get the best fit. Strangling the Cock, A.K.A. Cock Rings Feel free to ask me any questions you may have. Once we have a size range in mind I can recommend a few to start with.