Here is an oval gearwheel that fits Fischertechnik(TM) adapters.
You might call the shape elliptical, but strictly speaking the shape is not an ellipse.
The radius is a sinusoidal modulation vs. the circumfence.
The gear fits the fischertechnik hubs. The smaller and and larger diameter are 30 and 60mm, so they go along with fischertechnik's standard spacing.