same reason the permanent magnet means in an advantageous embodiment of the friction clutch 1 can be formed not by the permanent magnet ring 4 but by a plurality of ring segments which are situated on a circumferential line and are positioned spaced apart circumferentially or positioned concentrically with respect to the axis of rotation s of the shaft 6 the fundamental point for the formation of the desired permanent magnetic effect of the permanent magnet means is that the direction of magnetization should be the same or is permanently maintained in all the ring segments or segments of the permanent magnet means this arrangement should be distinguished in particular from systems for the formation of eddy currents and in particular has nothing to do with an eddy current system for example by means of an offset a running around the circumference which is part of the anchoring means and is formed on a radially inner side of a radially outer web 3 a of radially spaced webs 3 a 3 b of the belt pulley 3 a stop for an end 4 a of the permanent magnet ring 4 is provided in a correctly positioned mounted state it is thereby advantageously ensured that in the mounted state of the permanent magnet ring 4 which is mounted on web 3 a by means of a radially outer longitudinal side is fixed in position axially in one direction relative to a belt pulley base 3 c connecting webs 3 a and 3 b at its axially opposite end or at the free end of web 3 a the permanent magnet ring 4 is.