by the axial positioning of the holder 10 relative to the withdrawal end 2 in the shown embodiment three guiding pins 9 are provided with equal distances 120 u00b0 the guiding pins 9 are structurally and functionally separated from the permanent magnet pairs furthermore twelve regularly distributed 30 u00b0 permanent magnet pairs 13 14 are provided the number of guiding pins 9 and or of permanent magnet pairs as well may be selected differently although this is not shown in fig1 to 4 two ring shaped one piece permanent magnets could be provided instead of several single permanent magnet pairs 13 14 the ring shaped permanent magnets could be made e g from a mass which is bonded by plastic material and which can be magnetised in a further not shown modification of the embodiment of fig1 to 4 permanent magnet pairs could be used the permanent magnet of which pairs are attracting each other this could be realised e g by placing a ring like the outer ring 7 on ends of the guiding pins 9 which ends extended beyond the holder 10 and by mounting other attracting permanent magnets at the ring for example neodymium permanent magnets or ferrite permanent magnets are particularly suitable a detail variant of.