The one-piece cage for fixing device to an object by screwing blind to a plate or the like perforated by a square mounting hole, of the kind including that cage and, therein, a threaded part adapted to cooperate screw-fashion with a complementary threaded part to assure the required fixing, and comprising four identical radial lugs extending in two orthogonal diametral directions and whose profile is such that the resulting cross-shape can be inserted with a small clearance into the square hole, which cage is adapted to be inserted with a small clearance into the mounting hole and to bear on the edges of that hole at the end of the introduction of the cage therein, and is characterized in that it takes the general form of an elastically deformable U-shape having four lugs angularly offset at 90° to each other and adapted to receive contiguously between them the four lugs of the threaded part, the lugs being connected in pairs by two symmetrical bridges adapted to bear on the edges of the hole.