This is a small bearing-based wheel with a 12 mm iron ball. It is designed to create a “third wheel” on light miniQ robots.
The design consists of the ball itself, a plastic body, and 4 small iron bearings to reduce friction. The total height of when assembled is 16 mm.
The kit includes a set of fasteners to install the support on the miniQ frame. To create a stable robot one support is usually enough, although, depending on what your project is, you may need two - front and rear.