Cock Rings for Men

Cock rings are rings that are worn around the base of the penis and sometimes the testicles to make erections harder, bigger, and longer-lasting. They come in different materials, from flexible silicone and rubber to leather and metal.

While maintaining a hard erection is the primary function of a cock ring, bells and whistles, such as vibration or anal beads, offer up other fun uses — no penis required.
https://www.healthline.com/health/what-is-a-cock-ring-used-for#bigger-erections