A longitudinal plunging unit for a shaft assembly used for torque transmitting purposes. An adaptor is connected between the filtering part and a second cup. An auto-regulation can be achieved, whereby a second chamber is embodied as sensor for recording a pressure rise in the stomach and the control of the stoma constriction is achieved depending on the recorded pressure by means of displacement of the fluid from the chamber, or from the reservoir into the stoma-constricting chamber. When the second lower density layer is formed on the first higher density layer, a powder material layer for the lower density layer is formed at a predetermined thickness so as to have a thickness suitable for sintering condition and then the powder material layer is sintered to form the lower density layer.