| 摘要 |
The bolts 9, 10 are circular rings of diameter equal to that of the body of the post 5. The internal edge of each ring comprises as many notches as there are racks 6, 7. The width and the depth of each notch are only slightly greater than the width and the length of the rack teeth. The angular orientations of the notches are identical to those of the racks. The guiding collars 11, 12 have an annular shape and, at least partially, in front of the racks, areas having a vertical cross section in the shape of a U open towards the axis of the post. The bolts and the collars are slipped onto the post with the bolts being able to slide rotationally in the areas having a vertical cross section in the shape of a U. A lower control member and an upper control member, which are associated with the lower bolt and with the upper bolt, are used to rotate them individually. <IMAGE>
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