Back Spin

a.k.a. Loophole
Patented by F. Lammertink 1992, copyright 1991 Binary Arts.
(plastic, 6 inches diameter by 1.25 inches thick)

Two discs that can rotate with respect to each other hold a total of 35 balls in six three ball slots on each side, at any time one slot is missing one ball, creating a gap into which a ball from that slot can be rolled or a ball from the other side can be pushed through if the discs are rotated appropriately. The slots on each side are arranged as three spokes and three outer slots; the three colors of the balls in the spokes are the same as the three colors of the outer slots on the opposite side. Jaap's Page observes that this puzzle is relatively easy to solve by first solving the inner two balls of each spoke and then the remaining balls, essentially correcting one ball at a time.

Further Reading
Jaap's Page, from:
Lammertink Patent, from: - patent no. 5,172,912