A housing box for electrical connectors comprising: an arrangement of recesses (1) for receiving electrical contacts (2), and a secondary locking system (5) for the electrical contacts (2), such system engaging transversely behind the cylindrical envelope (12) of the contacts (2) in the recesses (1) in order to lock the contacts axially. The arrangement of the recesses (1) forms a central tower (3) in the housing. The secondary locking system (5) has a base (6) so disposed on the tower (3) as to be movable transversely to the axis of the contact between a first position in which retaining lugs (7) on the top edge of the base (6) are clear of the recesses (1), and a second position in which the retaining lugs (7) lock the electrical contacts (2) in the recesses (1).