Retention frame having separate plug-in modules (40, 40', 40") for a system plug connector having at least one such retention frame and an additional retention frame and a connector housing , wherein the plug-in modules (40, 40', 40") contain electrical contacts and are retained by the retention frames, wherein the retention frame has: a rectangular duct with devices for retaining the plug-in modules (40, 40', 40"), a plug insert which is arranged in the rectangular duct and within which the plug-in modules (40, 40', 40") can be inserted into the retention frame , wherein the plug-in modules (40, 40', 40") can be arranged so as to be able to be secured in the rectangular duct , characterised in that the retention frame further has slide rails which are arranged opposite and which are formed in the rectangular duct , wherein the retention frame is configured in such a manner that the plug-in modules (40, 40', 40") can be inserted at both sides, from an insertion side and from a connection side, perpendicularly to the retention frame into the rectangular duct , wherein the retention frame is further configured in such a manner that a plug-in module which is inserted into the plug insert and which has in each case at opposing sides two transverse ribs and a groove which is arranged therebetween, can be displaced within the retention frame transversely relative to the insertion direction laterally as far as a stop, wherein the slide rails engage in each case in the grooves , wherein the plug insert is constructed as a separate, U-shaped and electrically conductive portion and is in abutment with three sides within the rectangular duct of the retention frame , the plug insert has in the side frames thereof, which are orientated in a U-shaped manner, on the upper and lower edge two free-standing tongues which are arranged in a parallel manner and which are directed into the centre of the side frame and whose spaced-apart tongue ends are bent into the rectangular duct . a rectangular duct with devices for retaining the plug-in modules (40, 40', 40"), a plug insert which is arranged in the rectangular duct and within which the plug-in modules (40, 40', 40") can be inserted into the retention frame , wherein the plug-in modules (40, 40', 40") can be arranged so as to be able to be secured in the rectangular duct , characterised in that the retention frame further has slide rails which are arranged opposite and which are formed in the rectangular duct , wherein the retention frame is configured in such a manner that the plug-in modules (40, 40', 40") can be inserted at both sides, from an insertion side and from a connection side, perpendicularly to the retention frame into the rectangular duct , wherein the retention frame is further configured in such a manner that a plug-in module which is inserted into the plug insert and which has in each case at opposing sides two transverse ribs and a groove which is arranged therebetween, can be displaced within the retention frame transversely relative to the insertion direction laterally as far as a stop, wherein the slide rails engage in each case in the grooves , wherein the plug insert is constructed as a separate, U-shaped and electrically conductive portion and is in abutment with three sides within the rectangular duct of the retention frame , the plug insert has in the side frames thereof, which are orientated in a U-shaped manner, on the upper and lower edge two free-standing tongues which are arranged in a parallel manner and which are directed into the centre of the side frame and whose spaced-apart tongue ends are bent into the rectangular duct . <EOS>