Abstract: Mounted on the rotor 1 is a plate 10 which is connected to the rotor at a point 11 so as to be immovable in the direction of support but tiltable relative to the rotor 1. On one side, the plate 10 carries the sliding surface 4 for the mounting member 5 comprising the support surface 6 and, on its other side, the plate 10 forms the cross sectional surface 12 of a pressure cushion 13. The support surface 6 and the cross sectional surface 12 are located opposite each other and are substantially the same size. The pressure in the pressure cushion 13 and the pressure in the space between the sliding surface 4 and the support surface 6 are kept substantially the same as each other. As a result, the plate 10 and hence the sliding surface 4 remain flat even when deformation of the rotor occurs.