The shaft (20) has a proximal end (21) mechanically connected with an operational device, and a distal end (25) connected with a tool (50), where a plane from which center points of all cross sections of the shaft have a distance less than one-third of a diameter of the shaft is not provided in the shaft. A distal portion (24) and a center portion (23) lie in a plane, and a proximal portion (22) deviates from the plane of the distal portion and the center portion. The proximal end and the distal end are aligned parallel to one another or form an angle of 10 degrees to one another.