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1. A drive mechanism for a drug delivery device, comprising:
a lead screw comprising a first screw thread, a lead screw nut and a drive member, aligned with an axis defining an axial direction and an opposite axial direction, a coupling between the lead screw and the lead screw nut allowing a helical movement of the lead screw with respect to the lead screw nut at least in the axial direction, the drive member being rotationally locked with the lead screw nut, the lead screw being coupled with the drive member, the coupling generating a helical movement of the lead screw with respect to the drive member when the drive member is moved in the axial direction with respect to the lead screw, and the coupling being overridden to prevent a helical movement of the lead screw with respect to the drive member when the drive member is moved in the opposite axial direction with respect to the lead screw, spline features of the lead screw, the spline features being arranged in at least one row parallel to the axis with alternatingly small and large gaps between succeeding spline features, and a stop feature of the drive member, the stop feature facing the lead screw, a dimension of the stop feature in the direction of the axis being larger than the small gaps and at most as large as the large gaps. |
