is matched to the thickness of the wall 28 so that in the stop position the fingers 36 have completely passed through the opening 27 and their tips lie opposite an upper side of the lower wall 28 thus the blind nut 26 cannot be withdrawn from the opening 27 again without bending at least the fingers 36 in order to fasten the bumper stiffening 11 on the cross beam 14 the fasteners 15 are passed through holes 37 in the rear edge region 13 of the bumper stiffening 11 as shown in fig5 and screwed into the thread of the cylinder shaft 30 the length of the fasteners 15 is determined so that their tips each impact against the distal sections 33 of the blind nut 26 before the head of the fastener 15 presses the bumper stiffening 11 against the base plate 29 of the blind nut 26 in order to fasten the bumper stiffening 11 the fasteners 15 are thus screwed so far into the blind nut 26 that they splay the legs 31 apart on the other side in this way each blind nut 26 is anchored positively on the cross beam 14 but this tight fit can be cancelled if a downwardly directed tensile force acts on the blind nut 26 via the fastener 15 which is sufficiently strong to bend the upwardly diverging proximal sections 32 towards one another in a parallel orientation how large this tensile force is can be predefined exactly and reproducibly by selecting the wall thickness of the blind nut 26 and the shape of the legs 31 in the case of a collision in a medium velocity range preferably between 15 and 40 km h the bumper cladding 8 and the bumper stiffening 11 are pushed.