adapter 5 by means of an attaching clip and a locking clip the attaching clip 4 comprises a base plate separated into right 36 and left 38 sections by a thin walled flexible bridge 40 which has a hinge function to the right section 36 is joined a claw 37 at a right angle provided with an inwardly extending claw head 49 to the left section 38 is joined a left claw 39 at a right angle provided with an inwardly extending claw head 48 the attaching clip 4 is placed with its left right base plate section 38 against the external face of the adapter base plate 51 so as to make a retainer key 72 disposed at the interior face of left section 36 fit into a recess 55 disposed on the exterior face of the adapter base plate and the right claw head 49 fit into a recess 54 disposed at the external face of the right arm 53 of the adapter 5 then the left section 38 is swiveled around the flexible bridge 40 which forms a sort of hinge until it abuts the adapter base plate 51 thereby the right claw head 48 is inserted in recess not shown disposed on the external face of the adapter left arm 52 corresponding to recess 54 in fig2 4 the attaching clip 4 is shown in a state prior to it being clamped on adapter 5 the attaching clip 4 is locked on the adapter 5 by means of the locking clip 3 which comprises two faces an outwardly facing first face identical with the exterior face of a base plate 25 and.