Sphericon

The sphericon, or tetracon, is a developable roller. It has a single continuous, developable face such that it rolls along a plane with every point on its face touching plane. It is the simplest roller in both the polycon and polysphericon classes. It is also a two-disk roller.

It can be constructed from a bicone with an apex angle of $$\pi/2$$, by dissecting it in half along a plane passing through both apexes, rotating one half by $$\pi/2$$, and recombining the two halves along their square faces. It can also be constructed as the convex hull of two perpendicular half circles sharing a center.