Spirograph, a geometric drawing toy, was introduced to the United States' market by Kenner, Inc. in 1966.
It consisted of a set of plastic gears and other shapes such as rings, triangles, or straight bars. There were several sizes of gears and shapes, and all edges had teeth to engage any other piece. For instance, smaller gears fit inside the larger rings, but also can engage the outside of the rings in such a fashion that they rotate around the inside or along the outside edge of the rings.
To use it, a sheet of paper was placed on a heavy cardboard backing, and one of the plastic pieces was pinned to the paper and cardboard. Another plastic piece was placed so that its teeth engage with those of the pinned piece. The point of a pen was then placed in one of the holes in the moving piece. As the moving part moved, the pen traced out a curve. The actual number of arrangements possible by combining different gears was very large.