shaft 17 at one end of the drum 2 so that pushing on the lever 10 results in rotation of the shaft 17 the lever 10 is used here as an example and serves to secure the shaft 17 so that it cannot turn relative to the bearings 12 and 14 of the drum parts 4 and 5 other mechanisms for securing the shaft 17 so as to prevent turning are feasible for this purpose the lever 10 has two lever arms 100 that embrace the shaft 17 whereby a pin 25 connects both lever arms that secure the shaft 17 to one another and assures that the lever arms 100 embrace the shaft 17 securely and tightly so that the lever 10 is clamped to the shaft 17 securing the lever 10 to the shaft 17 with the lever arms 100 assures that a movement of the lever 10 is converted to a rotation of the shaft 17 when the shaft 17 is rotated by the lever 10 the diameter of the drum 2 is changed as described below the drum parts 4 and 5 are moved toward one another in the direction of the arrow by rotation of the lever 10.