The invention relates to a plug-in system for tailer vehicles provided with an automatic coupling system of the supply lines, comprising a plug (1) supporting the line contacts (1a) and a socket (2). Said plug (1) comprises guide elements (4) that actively engage when approaching the guide elements (5) of the socket (2). The invention also relates to a plug half. The aim of the invention is to improve a plug system, in particular a plug half (1) for an automatic coupling system of supply lines on an articulated train in relation to its centering during the coupling process. Said aim is achieved by virtue of the fact that the guide elements (4) comprise a main guide pin (6) and at least one centering pin (7a, 7b) that is arranged at a distance therefrom. At least the centering pin (7a, 7b)and/or the associated guide element (5, 9) is elastic in the radial direction.