supported on the upper platform of the machine while all the remaining components are mounted between the machine and the lower bracket 14 as clearly seen in fig5 in the preferred embodiment shown in fig8 through 19 the following variations have been introduced the upper plate is now formed by two superposed parts 4 and 4 39 defining a cavity 45 to house a faceted head 46 of a retaining screw engaged in the threaded hole 47 at the end of the stationary shaft 13 the shaft 13 has a ring stop 48 acting as a seat for a coaxial bearing 49 paired with a similar bearing 50 and a completed with other two needle bearings 51 fig8 and 9 a rod 46 39 extends from the faceted head 46 and projects above the plate 4 the bushing 25 is firmly connected to the small flat plate 29 39 the shape of which is illustrated in fig1 it can be seen that the plate 29 39 forms a box 52 which is open downwards and the ratchet 34 39 is contained within the box 52 this ratchet 34 39 has on its upper surface a stop 53 and one end thereof is in the form of an inclined plane 54 this ratchet 34 is hinged on a pin 33 39 fastened to the box 52 in the plate 29 39 a driving radial strip 55 which is a part of a disk 56 attached to the second plate 57 having also a disk like shape projects between the stop 53 and the inclined plane 54 this small plate 29 39 is firmly connected to the bushing 25 fig8 while the assembly 56 and 57 can move freely around the inner stationary shaft 24 passing through the bore.