Surf and Taz42o are correct. It absolutely is not a Caltrop (also know as a horse-crippler, and a Crow's-Foot). Nor is it a Ninja-weapon. Deldave's find is one version of several varieties of "Mill-Stars"... which is a type of Tumbler Media used in the Metalcasting industry to remove burrs and casting-sand from raw-out-of-the-mold metal castings.
As Taz42o said, the defining characteristic of an actual Caltrop is that a Caltrop always has a Tetrahedral form, an arrangement of FOUR sharp-tipped spines which will always land on the ground with one spine sticking STRAIGHT upward, to impale a horse's hoof of a soldier's foot -- or tires. See the two illustrations, below.
You can't make these 6-armed Mill-Stars sit with one arm pointing straight upward. They sit with the arms at a 30-degree angle -- which means you could drive over one and it won't pierce the tire. Or, step on one and it won't pierce your shoe.
Surf already posted a photo of an actual Caltrop. To see more photos (note that they always have only 4 spines), and learn about them, go here:
Caltrop - Wikipedia, the free encyclopedia
Here are some photos of other variations of Mill-Stars. Note that none have 4 arms/spines. I'll also include a drawing from an Army OSS Manual showing an actual modern-era Caltrop being used for sabotage.
