Unipolar or multipolar electrical plug connectors include contact carriers having contact chambers, into which contact elements can be inserted. These contact elements latch with so-called snap-on lances. In the present SYSTEM, the latching is produced by a part of the contact element with a snap-on lance, a smooth outer geometry of the contact element being present in the assembled state, but by latching of a non-resilient snap-on lance within the contact chamber. Consequently, the advantages of the snap-on lance locking mechanism unite with those of the clean-body construction.