Abstract: There is disclosed an elongate housing member of insulating material defining a downwardly open interior space for reception of a conductor strip so as to form an electric current conductor rail with the strip, the housing member being provided at each of two opposite sides thereof with a respective longitudinally extending rib. The ribs are arranged and constructed in such a manner that the housing member can be connected to a further such housing member at substantially the same height. One of the ribs is provided at its underside with a groove and the other rib with an upwardly projecting bead, the groove and bead having substantially the same cross-sectional shape.