This is a small cap to cover the central hole in Toyota Prius wheels from the Gen2 line. The "Touring" model has nice-looking alloy-spoke wheels and you can dispense with the factory hubcaps -- but the axle bolt remains visible. This little cap fits in the center of the wheel and snaps into the same small interior groove that holds the center of the factory cap in place.

You can customize it with your own logo/initials/whatever, of course!