A nut assembly for engaging external threads a lead screw comprising: a nut member (110, 210) including: an annular base portion (120, 220); and at least a first flexible finger (122, 222) and a second flexible finger (122, 222) joined to the base portion (120, 220), each of the first flexible finger (122, 222) and the second flexible finger (122, 222) extending axially from the base portion (120, 220), each of the first flexible finger (122, 222) and the second flexible finger (122, 222) extending between a first end joined to the base portion (120, 220) and a second free end; and threading on an inner periphery of the first and second flexible fingers (122, 222) for engaging with the external threads of a lead screw; an adjustment arrangement including: a cap member (150, 250) extending around the first and second flexible fingers (122, 222); characterized in that the adjustment arrangement further comprises a first adjustment member (152, 252) movably mounted to the cap member (150, 250) to move radially relative to a central axis of the nut assembly, the first adjustment member (152, 252) biasing the first flexible finger (122, 222) radially towards the central axis of the nut assembly; and a second adjustment member (152, 252) movably mounted to the cap member (150, 250) to move radially relative to the central axis of the nut assembly, the second adjustment member (152, 252) biasing the second flexible finger (122, 222) radially towards the central axis of the nut assembly, the radial positioning of the second adjustment member (152, 252) being independently adjustable from the radial positioning of the first adjustment member (152, 252). a nut member (110, 210) including: an annular base portion (120, 220); and at least a first flexible finger (122, 222) and a second flexible finger (122, 222) joined to the base portion (120, 220), each of the first flexible finger (122, 222) and the second flexible finger (122, 222) extending axially from the base portion (120, 220), each of the first flexible finger (122, 222) and the second flexible finger (122, 222) extending between a first end joined to the base portion (120, 220) and a second free end; and threading on an inner periphery of the first and second flexible fingers (122, 222) for engaging with the external threads of a lead screw; an annular base portion (120, 220); and at least a first flexible finger (122, 222) and a second flexible finger (122, 222) joined to the base portion (120, 220), each of the first flexible finger (122, 222) and the second flexible finger (122, 222) extending axially from the base portion (120, 220), each of the first flexible finger (122, 222) and the second flexible finger (122, 222) extending between a first end joined to the base portion (120, 220) and a second free end; and threading on an inner periphery of the first and second flexible fingers (122, 222) for engaging with the external threads of a lead screw; an adjustment arrangement including: a cap member (150, 250) extending around the first and second flexible fingers (122, 222); characterized in that the adjustment arrangement further comprises a first adjustment member (152, 252) movably mounted to the cap member (150, 250) to move radially relative to a central axis of the nut assembly, the first adjustment member (152, 252) biasing the first flexible finger (122, 222) radially towards the central axis of the nut assembly; and a second adjustment member (152, 252) movably mounted to the cap member (150, 250) to move radially relative to the central axis of the nut assembly, the second adjustment member (152, 252) biasing the second flexible finger (122, 222) radially towards the central axis of the nut assembly, the radial positioning of the second adjustment member (152, 252) being independently adjustable from the radial positioning of the first adjustment member (152, 252). a cap member (150, 250) extending around the first and second flexible fingers (122, 222); characterized in that the adjustment arrangement further comprises a first adjustment member (152, 252) movably mounted to the cap member (150, 250) to move radially relative to a central axis of the nut assembly, the first adjustment member (152, 252) biasing the first flexible finger (122, 222) radially towards the central axis of the nut assembly; and a second adjustment member (152, 252) movably mounted to the cap member (150, 250) to move radially relative to the central axis of the nut assembly, the second adjustment member (152, 252) biasing the second flexible finger (122, 222) radially towards the central axis of the nut assembly, the radial positioning of the second adjustment member (152, 252) being independently adjustable from the radial positioning of the first adjustment member (152, 252).