Abstract: Gripper devices transfer covers from a magazine onto filled packing containers guided along a substantially horizontal transport trajectory. The gripper devices are on a supporting shaft which is driven via a rod system 18 by a grooved cam plate and a roller lever interacting therewith. By shortening the effective lever arm of the roller lever with the use of an adjusting unit coming into operation when the cover mounting device is blocked, the articulation point of the rod system in an elongated slot of the roller lever is altered in such a way that the stroke movement of the rod system and thus of the supporting shaft and of the suction elements or gripping devices becomes shorter, i.e. a short stroke occurs, thus ensuring that no further covers are extracted from the magazine and placed on the packing container.