In an extruder wherein the slip-on elements (1) have a cross-sectional profile comprising circular arcs corresponding to the maximum slip-on element diameter, the slip-on element core diameter and the center distance of the slip-on elements (1), the slip-on element (1) has no shaft-to-hub connection in the area of the circular arc corresponding to the slip-on element core diameter and/or it is provided at its ends with reinforcement segments (13, 14).