The Wartenburg Wheel is a tool used by neurologists to test nerve sensitivity. Made of stainless steel, the 20 sharp points on the wheel can be rolled over the skin with varying levels of pressure for different sensations.
For those into sensory play, this is a very basic, but also incredibly versatile tool. Try rolling it gently along the inside of someone's arm or the soles of his feet or—well, you decide. Some say the feeling is more intense when blindfolded.
Please note: The points are not sharp enough to puncture skin unless excessive pressure is applied. Do not press hard enough to puncture the skin.