The material selected for the cylinder 9 is a steel or aluminium pipe or hard plastic, like PVC or polyamide, for example but other materials could also be used. The screw 10 is made of brass or steel and the nut 2 with the guide 3 are bronze or steel. The frame and gears are made of the materials commonly used for such purposes in the fine mechanics – brass, steel, PVC, etc. The hinges and arms are steel. The tanks for the hydraulic brake are aluminium or plastic and the blade 19 is made of aluminium or laminated fabric as well as thin steel sheet. Parts not mentioned so far are made of the same materials as those described under Figure 1, 3, etc.