Abstract: The invention relates to an open-end rotor spinning unit and particularly solves the problem of the relationship between a fiber defining stud of a separator, a fiber supply duct and a yarn take-off duct passing through the separator and the stud.According to the invention, there is established a dimensional relationship of the defining stud to the mean staple length of fibers, and the orientation of the supply duct at an acute angle to the front wall of a cylindrical projection partially engaging into the spinning rotor.In inner section of the peripheral wall of the defining stud is curved in the direction of a natural fiber flow trajectory into the direction of the spinning rotor rotation while the outer section is either in contact with or radially set back from the cylindrical wall of the projection at a distance of up to 4 millimeters from the edge of the wall.