Clamps
Nipple clamps are designed to fit directly on the nipple and are called "sensation play" sex toys. Clamps create sensations people find both uncomfortable and pleasurable at the same time.
When a clamp is first applied, there is often a feeling of pinching or pressure. In time, this sensation lessens and the area can feel numb or dulled. Once the clamp is removed, the wearer will feel another rush of intense sensation and sensitivity.