A connecting part for attachment on a mounting rail has a fastening part with an at least approximately rectangular cross-section. The fastening part has legs and surrounds when mounted a mounting rail on all sides by having a matching cross-section formed by the legs. The fastening part has clamping devices for effecting a clamping fixation of the connecting part on the mounting rail. A cross-sectional plane of the fastening part has two diagonally opposed corners and the clamping devices are arranged on the two diagonally opposed corners, respectively.