the extrusion head comprises a first extrusion outlet surrounding an aperture wherethrough a metal section can be fed and a second extrusion outlet located externally to the first extrusion outlet , the latter being communicated to a first feed branched channel for the plastics material to be extruded , extending substantially perpendicularly to the feed direction of the metal section , while the second extrusion outlet is in turn communicated to a second plastics material branched channel also perpendicularly extending to the feed direction of the metal section and substantially juxtaposed to the first channel .