Cock rings are used to help strengthen and maintain a rock hard erection. They work by letting blood flow in the penis, and blocking it in. Some people also use cock ring for BDSM play. Different cock rings have different roles. Some cock rings have clitoral bumpers or stimulators to help during intercourse. Other are made to fit the base of a penis pump, and are used in conjunction with such devices (to help maintain the erection created from the penis pump suction).