An open end spinning device or a false twisting device having two mutually parallel pairs of rollers for driving a spinning rotor or a twisting tube and a horseshoe-shaped magnet associated therewith for retaining the twisting tube or rotor in a wedge-shaped nip between the pairs of roller, each pole of the magnet acting on a collar on the rotor or twisting tube and being provided with a recess extending parallel to the axis of rotation of the rotor or tube and having a semi-circular cross-section to receive the collar is provided with a magnet having one pole shaped so that upon axially displacement of the rotor or tube away from its normal position by pull of the thread each of the collars still lies opposite the magnet at least at the base thereof.