A switching device in a system of switching devices, which can be coupled to mountable switching, auxiliary switching, or signal devices. In the case of a cylindrical, manually operated part, disposed in the housing, having a selector, a coupling element pair comprising a jaw-shaped coupling element and a cone-shaped coupling element are provided on the cylindrical part in the direction of the switching axis on a mounting side, the pair of coupling elements being movable behind a housing slot, and being forced in engagement connection with each other and arranged in a housing slot on the surface of a device to be attached.