These Nipple clamps with chain (pair) 'The clover clamp', also referred to as a "butterfly clamp", is of Japanese design and has the ability to provide increasing tension if pulled on. The clamp itself is flat, but about 10 cm by 5 cm in size. Using spring tension, the clamp is applied to the nipple and the tension of its spring holds the clamp in place. This clamp usually provides a very high pain level, and is usually only used by more advanced users. To increase tension on the nipples, small weights such as fishing line sinkers can be attached to the ends of the clamp. As increased pulling tension is applied to the clamp, it will cause the jaws of the clamp to close tighter depending on the amount of pull pressure. Another method is to use the clamps to keep a person in one place. If cord is tied from the clamp to a fixed place, the wearer of the clamps cannot move away because the clamps will tighten as they try to move. Eventually the clamps would be pulled off the nipples, but not before considerable pain and discomfort is felt.