From the campaign:
SpinPins are metal pins that contain a back piece with an arrow and a free spinning front piece with a random element such as numbers. By spinning the front, you can randomly select one of the numbers on it (similar to a prize wheel or wheel of fortune wheel). The pin back allows them to easily attach to a bag, shirt or jacket. By ensuring the varied distribution of numbers around the wheel and by keeping the wheel a uniform weight, SpinPins produce a fair random number when spun.
SpinPins are about 1.5" in diameter and weigh about 1.5 ounces. They attach in the back via a butterfly clasp. While they're not nickel-free, you can get a rubber backer instead of the traditional metal clasp. It doens't prevent the pin from spinning as much, but it does mean the part that makes contact with the interior of your shirt, bag, etc is nonmetallic.