vis u00e0 vis the hole 42 in a preferred embodiment the hole 42 on the branch 32 approximately normal to the axis of insertion is a circular hole whose dimensions correspond to the diameter of the plug 22 except for the dimensional tolerances for example for an is 1 distal plug the dimension is 1 59 u2212 0 03 mm and for a df1 distal plug the dimension is 1 25 u2212 0 03 mm the hole 34 the second branch 44 which extends obliquely to the z axis of insertion is an oblong hole so that it can also be crossed except the dimensional tolerances by the plug inserted along the z axis of insertion as can be seen in greater detail in fig4 a and fig4 b the holes 42 and 44 are slightly shifted with respect to each other when the leaf spring is in the free state that is to say in the absence of any external forces and before insertion of the plug 22 see fig4 a however these holes are aligned when the plug is inserted the leaf spring 30 then being in a deformed state of elastic stress see in fig4 b this alignment of the holes geometrically defines a channel through which the cylindrical plug 22 can be inserted housed and kept in place the.