annular shoulders application_number US 71675800 A description referring now to the accompanying drawings and initially to fig1 an open end spinning unit is identified as a whole by the reference numeral 1 in a known manner the spinning unit has a rotor housing 2 in which the spinning cup of a spinning rotor 3 rotates at a high number of revolutions the spinning rotor 3 is integrally mounted coaxially to a rotor shaft 4 supported in the bearing wedge of a support disk bearing arrangement 5 and is driven peripherally by a tangential belt 6 extending over the length of the machine and held frictionally against the shaft 4 by a contact roller 7 the rotor shaft 4 is axially fixed by means of a permanent magnet axial bearing 18 shown in detail in fig2 and 3 as is customary the rotor housing 2 is open toward its front and is closed during operation by a pivotably seated cover element 8 into which a channel plate not shown in detail with a seal 9 has been cut the rotor housing 2 is also connected via an appropriate aspirating line 10 to a suction source 11 which generates the underpressure required in the rotor housing 2 a channel plate adapter 12 is arranged in the cover element 8 which holds a yarn withdrawal nozzle 13 as well as the mouth area of a fiber guide conduit 14 a small yarn withdrawal tube 15 follows the yarn withdrawal nozzle 13 in addition an opening roller housing 17 is fixed in place on the.