A connector system of a structural frame work for display structures, the system comprising a socket device and a plug device that can be coupled to the socket device, the socket device including an outer housing and a socket member in the socket housing, the socket member having a socket hole of non-circular cross-section disposed in a distance behind a coupling hole that is bordered by a retainer wall of the outer socket housing, the plug device comprises a plug body and a coupling sleeve slidably and rotatably fitted onto the plug body that includes an exposed plug end portion axially projecting out of the coupling sleeve to fit into the socket hole of the socket member, the coupling sleeve including at least one radial locking nose projecting outwardly from the free end portion of the coupling sleeve that fits through the coupling hole of the socket housing when the coupling sleeve is in a release position, the plug body and the coupling sleeve include axial cam members engaging each other to cooperate upon a rotation of the coupling sleeve for an axial displacement of the coupling sleeve between the release position and a coupling position so that the plug end portion of the plug member can be fitted into the socket hole of the socket member while the free end portion of the coupling sleeve is inserted through the coupling hole into the socket housing, and the locking nose is displaced towards and against the retainer wall of the socket housing upon a relative rotation of the plug device and the socket device.