A system having a plurality of plug-in connectors each with a housing, the shape of the housings differing such that the housings have first housing parts which, at least in terms of the interface connections to second housing parts, are identical to the other components of the particular plug-in connector, and second housing parts having identical connecting means for connecting with the first housing part, and differ slightly in the external shape which serves to form a coding by which the individual positions of the individual plug-in connectors on or in the multiple housing are assigned.