The component top side (2) serves for cooperation with other components. Under the top side is located a downwards-open hollow body (1) contg. a wheel (4) for the component mobility. Pref. the wheel is partly immersed in the component hollow body. Pref. the wheel is releasably mounted in two bearings (7). The top side may comprise four vertical cylinders, cooperating with undersides of other components. In the wheel travelling direction other wheels may be provided in tandem on adjacent configurations.
