Abstract: A device for controlling the rectilinear translation of a movable member, comprises a screw engaged by a nut having cooperatingly shaped thread surfaces the dimensions of which are such that there is a radial clearance between the screw and the nut and an axial clearance between adjacent helical flanks of the screw and the nut. The nut is provided with radial passages communicating with the chambers defining the radial clearances, which can be put into communication with a source of compressed gas enabling the formation of an air cushion or air bearing between the two relatively movable members thereby reducing the turning moment necessary for effecting rectilinear movement of the movable member.