A metal frame made up of a plurality of linear bars, which have a constant cross section, are obtained by extrusion, and are joined to one another by means of welding at structural nodes defined by jointing bodies provided with pockets for housing the linear bars. The jointing bodies have box type structures and are made up of the union of respective a load-bearing element, which is obtained by extrusion and has a given direction of extrusion, with a pair of plane closing metal sheets, which are set perpendicular to the direction of extrusion and are welded to the load-bearing element on opposite sides of the load-bearing element. The load-bearing element may also be formed by the lateral union of a number of simple elements, each of the simple elements being obtained directly via extrusion and having a given direction of extrusion parallel to the direction of extrusion of the other simple elements, and wherein the simple elements are joined to one another laterally by mechanical slots.