Abstract: The invention relates to an extension plug-in unit comprising a socket (2) connected to a first cable (1) and a plug (4) connected to a second cable (3), said plug (4) and socket (2) having cooperating contact means (5, 6) comprising male and female contacts for electrical connection of the first cable (1) to the second cable (3) and cooperating connecting means (7, 8, 9) for joining the plug (4) mechanically to the socket (2). To enable a mechanically simple and reliable construction, the male and female contacts (5, 6) are disposed to be located substantially in succession in the axial direction of the cables (1, 3), and the mechanical contact means comprise hinge means (7, 8) at one end of the plug and the socket for articulated joining of the plug and socket and locking means (9) at the other end of the plug and the socket for locking the plug (4) and socket (2) together at said ends when they are pressed against one another.