A load carrying assembly for use with a pick-up truck having a load carrying bed, includes a first load bearing structure and a second load bearing structure which are both mounted to the truck above the bed. The structure includes a cross member and a pair of spaced apart upright support members. The structure includes a cross member and a pair of spaced apart upright support members. The assembly further includes an interlocking system comprising connecting formations in the form of bolt holes defined through the members and nuts and bolts for releasably bolting the structures to one another in an arrangement wherein certain members abut one another, thereby to form a unitary combined load bearing structure to provide for enhanced stable support of the load by the structure.