performed by the tappet 17 a is being damped so that the tappet 17 a is again centered relative to the central longitudinal axis 9 of the casing 8 a after disappearance of the transverse load component in case of a transverse load component of great amplitude the motion of the outer rib portion 52 a is defined by the stop 55 a the following is a description of a third embodiment of the invention taken in conjunction with fig8 and 9 identical parts have the same reference numerals as in the first embodiment to the description of which reference is made parts that differ in construction but are functionally identical have the same reference numerals with a b annexed the substantial difference from the first embodiment resides in the configuration of the guiding damping unit 41 b like in the first embodiment the guiding damping unit 41 b is fixed to the cap 39 b unlike the first embodiment the cap 39 b is not pushed over the casing cup 27 but into it so that the locking noses 43 b that are disposed on the cap 39 b stand out radially snap engaging from inside with corresponding recesses in the casing cup 27 the cap 39 b comprises four damping elements 50 b which are uniformly distributed along the circumference and project inwards from an annular edge 68 the inner rib portion 51 b as well as the connecting rib portions 53 b constitute a flexibly compressible spring arm or bow which projects inwards.