The most basic cock ring provides a simple function - it makes him harder, more sensitive, and last longer. Rubber or silicone cock rings are designed to stretch to encompass the girth of his shaft or the base of his balls. Most guys only put the cock ring around their shaft. But if he's willing, he can pull his testicles through too - most are designed for it. Once the blood flow is restricted, he’ll feel the pleasure and sensitivity in his balls, not just his penis.