having a typical wall thickness of about 0 028 to 0 075 inches and preferably about 0 044 inches is especially preferred the required strength of the reinforcing beam depends on whether the seat belt retainer is to be mounted on the seat mechanism the remainder of the structure illustrated in the drawings is largely conventional and needs but little modification to accommodate the present invention the base structure transferring the harness forces including those from the reinforcement beam 2 to the body structure of the vehicle includes the seat recliner 9 which includes a pivot latch mechanism the seat tracks 12 and the riser brackets 13 the usual seat belt latch receptacle 14 is illustrated in fig2 and is attached to the base of the seat at the side opposite the belt retractor the latch receptacle 14 engages buckle 40 of the combination lap and shoulder belt harness 11 the riser brackets on the outside are bolted by bolts 42 to door sill 44 the rocker section 15 defines the bottom of the door opening outboard of the frame structure to which the seat base is attached the inboard bracket 47 of the seat support structure can be mounted at the central tunnel.