with an external thread 29 in a central region and with an adjustment element 31 on one outer end 30 the adjustment element 31 in particular is embodied as manually operated wheel wherein electric pneumatic or hydraulic embodiments of the adjustment element 31 are also suitable for adjusting the actuator 23 via remote control coaxial to the adjusting spindle a flange 32 is arranged in the axial direction on the outside of the machine frame 20 and contains a central bore 33 with an internal thread 34 the adjusting spindle engages with its external thread 29 in the internal thread 34 of the flange 32 a rotation of the adjusting spindle causes it to be displaced in the axial direction a since the bolt 21 is fixed in the axial direction relative to the adjusting spindle a turning of the adjustment spindle consequently causes a displacement of the bolt 21 in the axial direction a a locking nut 35 surrounds the adjusting spindle in the axial direction on the outside of the flange 32 the locking nut 35 is provided with openings 36 embodied to extend radially at an angle toward the outside into which a clamping element 37 can be inserted if the clamping element 37 is screwed into the locking nut 35 until it reaches the external thread 29 of the adjusting spindle and fits flush against the machine frame 20 it prevents a further and unintended screwing in of the adjusting spindle in the radial direction.