Lead screw nut

A nut for a lead screw comprising an inner annular member, an intermediate annular member and an outer annular member, the inner, intermediate and outer annular members being concentric and when aligned having common axes, the inner annular member being within the intermediate annular member, and the intermediate annular member being within the outer annular member, in which the inner annular member an outer convex spherical periphery and the intermediate member has an inner spherical concave periphery, the peripheries being concentric with the center, and the inner periphery of the intermediate member being engaged against the outer periphery of the inner annular member, the intermediate member being constrained to rotate about the inner annular member on a first axis perpendicular to the common axis, and in which the intermediate annular member has an outer convex spherical periphery and the outer annular member has an inner spherical concave periphery, the peripheries being concentric with the centre, and the inner periphery of the outer member being engaged against the outer periphery of the intermediate member, the outer annular member being constrained to rotate about the intermediate annular on a second axis perpendicular to both the common axis and the first axis:

• where the inner annual member has a central bore with an internal screw thread and the outer annular member has at least one pair of parallel external surfaces;
• the parallel external surfaces supported in sliding contact with co-operating surfaces of a pair of opposed support pieces mounted in a frame.