A cock ring, or cockring, is a ring that is placed around a man's penis, usually at the base, primarily to slow the flow of blood from the erect penile tissue, thus maintaining erection for a longer period of time.
Cock rings can be worn around just the penis or both the penis and scrotum, or just the scrotum alone, though this is usually called a testicle cuff. Rings can be made of a variety of different materials, most commonly leather, rubber, or silicone, though nylon and metal are also used either as the main component or part of the closure.
The term cock ring is sometimes used as a synonym for a Prince Albert piercing, a piercing of the penis that is usually, though not always, a metal ring.
A man may wear a cock ring because he has erectile dysfunction (ED), erectile hyperfunction, or otherwise wants to prolong erection because he likes the particular sensation of tightness and extreme engorgement that wearing one provides. It can be worn as a sex toy, as genital jewelry, or simply for the appearance. When used for ED, a vacuum pump is used to produce an erection in spite of vascular or nerve damage, and the ring slid off the pump's cylinder onto the base of the penis to maintain the erection.
Some men enjoy using cock rings for masturbation, as wearing of this sex toy contributes to better erection and delays orgasm, thus it intensifies orgasmic sensations. Also vibrating cock rings deliver a great range of very pleasurable vibrations that enhance enjoyment.
The purpose of a cock ring is to trap blood inside the penis in order to maintain an erection, or encourage a stronger erection. In order to do this it must be placed at the base of the penis.
For rings made of elastic material, it may simply be stretched over the penis and scrotum and situated against the body. However, with rigid rings made of plastic or metal the process is different. First each testicle is fed through the ring and the entire scrotum is pulled through, then the flaccid penis is pushed through the ring and situated against the body. 
Some models include a protruding clitoral stimulator, designed to tickle the clitoris, vulva, or anus during sex. Others, such as the vibrating ring, vibrate, either vibrating the ring itself, or in a popular 'Dolphin' variant using two removable bullet vibrators to provide stimulation to the testicles and clitoris. Some cock rings have vibrators attached that can be worn to stimulate the scrotum or perineum of a partner during sexual intercourse. Many women find that rings with vibrator attachments provide clitoral stimulation that is needed for achieving orgasm. Cock ring users should keep in mind that any pain, discomfort, or feeling of coldness in genitals is a signal to take the cock ring off.
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