Abstract: The device is made up of a double-action jack (4, 5, 6, 7, 12, 13), a case (9), a tip (10) and a fixing means (11). A rack (15), integral with the piston (12) of the jack, rotatingly drives a pinion (17) guided by two bearings (23, 24). On the fluted end (36) of the shaft (22) of the pinion there is fixed a swivel arm (2) having an axis perpendicular to the axis of articulation (18). This axis forms with the axis (16) of the rack an angle .alpha. other than 90 degrees. Owing to this angle .alpha., the swivel arm and a small wheel (3) attached thereto, when swivelling from a retracted position to an engaged position, move in a plane which is oblique relative to the horizontal, even though the cage (1) of the device may be placed in such a way that its axis is horizontal.