respect to the section plane in fig1 and 2 the fixing device 16 illustrated in fig3 and 4 comprises an open iron circuit 5 a permanent magnet 6 and a magnetic disconnection coil 15 the open iron circuit comprises three preferably fixed individual iron parts 5 a 5 b and 5 c the first iron part 5 a and the second iron part 5 b are connected to one another via the permanent magnet 6 while a third iron part 5 c is arranged offset upwards with respect to the first two iron parts 5 a and 5 b this third iron part 5 c is surrounded by the magnetic disconnection coil if as is illustrated in fig4 two holding elements 7 7 u2032 which are formed from ferromagnetic material or iron rest on side contact surfaces of the open iron circuit 5 the open iron circuit 5 and the holding elements 7 and 7 u2032 form a closed iron circuit the magnetic lines of force produced by the permanent magnet 6 now run in the closed iron circuit and thus form a closed magnetic field circuit in the present magnetic iron circuit the holding elements 7 and 7 u2032 are each fixed at two points specifically their respective contact surfaces with the two iron parts 5 b and 5 c on the fixing device 16 the splitting of the permanent magnetic holding force which is produced by the permanent magnet flux between four series connected holding surfaces in the closed iron circuit results in multiple use of.