Cover parts are known that are manufactured with a through-opening in the radial direction which is intended for passing a portion of a blade therethrough. More precisely, the blade is guided so far into the opening that the blade protrudes on the other side of the cover part. The blade is then typically soldered or welded firmly to the cover part, and, if appropriate, the projecting portion of the blade is cut and ground down in order to produce an essentially smooth surface.