point of the conveyor end 24 of the advance element 20 are altered vertical displacement of the pivot axis 36 downwardly increases the upper lever length of the advance element 20 and the lower lever length at the drive side is correspondingly shortened as a result the advance stroke of the conveyor end 24 of the advance element 20 is increased displacement of the pivot axis 36 upwardly shortens the upper lever portion of the advance element 20 and increases the length of the lower lever portion whereby the advance stroke of the advance element 20 is reduced the horizontal adjustment component causes displacement of the engagement point of the conveyor end 24 of the advance element 20 into the clip line 2 towards the right or the left respectively if the pivot axis 36 of the adjusting device 30 is on a notional perpendicular line extending through the axis 12 of the drive unit 10 the conveyor end 24 of the advance element 20 describes an ellipse the major axis of which also extends through that perpendicular notional line the point of the highest vertical stroke movement of the clip line 2 is on that line the engagement point of the conveyor end 24 into.