A ball stretcher is a male sex toy that is used to stretch and elongate the scrotum. These devices are meant to wrap around the base of the scrotum and may come with attached cock rings.
Although ball stretchers are sometimes used during cock-and-ball torture scenes, many men also find the sensation of having their testicles gently pulled away from the body very pleasurable. Regularly using ball stretchers can also permanently elongate the scrotum, which is a look that some men and women find attractive.
Remember, the ball stretcher has to be tight enough or else the stretcher would slip off. At the same time, you don’t want it to be too tight. For most men, the ball stretcher diameter should be about 75 to 80% of their ball diameter. Anything smaller than that, and it may be too tight for you to wear.
With this in mind, measure around your sack just above your balls with a tape measure or a string to get the circumference.
Then divide that by 3.14 to get the inside diameter
Then convert your inches measurement to millimetres