to ensure that a cross element forming an attachment tube or rod extending across the back portion of a motor vehicle , can absorb energy if an object impinges against a net suspended from the attachment rod or tube , a tubular insert element is located in a chamber formed in the end of the cross element , to which a kinetic energy absorbent deformation structure is coupled . the deformation structure may be another tubular body , for example a plastic injection - molded part . a shaft having a coupling end for attachment to a holding bracket for coupling the cross element to the vehicle is formed with radially projecting ears which , upon impingement of an object against the net , will cause the shaft to withdraw into the deformation body , causing deformation thereof and thereby absorbing kinetic energy . a spring , under normal conditions , holds the shaft in one of two extreme positions . the deformation body and the insert element , being of plastic , receive the shaft snugly , thereby preventing rattles ; the presence of the spring additionally ensures that no rattles occur upon movement of the vehicle .