the radially upper layer 32 of the tread 3 in the non vulcanized state the same applies to the inserts 12 and 13 for the radially inner layer 31 which is obtained separately by extrusion or for the layer 6 fig2 shows a first extruder 10 which using the extrusion screw 101 delivers the non vulcanized rubber mix intended for the manufacture of the upper part 32 of the tread in an extrusion head 102 defined by upper 104 and lower 103 arches and comprising a flow channel 105 which firstly carries the mix to the rotary roller 15 which is associated with the extruder 10 and secondly carries said mix towards an extrusion orifice 107 defined by the cylindrical surface 150 of the roller 15 and the fixed wall of a blade 106 the extrusion orifice making it possible to impart the desired profile to the extruded mix with said first extruder and roller there is associated a micro extruder 40 mounted fixedly on a support 41 this extruder equipped with a screw 401 and an extrusion head 402 comprises at its end a nozzle 403 fixed to the die of the micro extruder 40 and intended depending on the desired profiles and traces to extrude the circumferential insert 11 in the profiled member of hot non vulcanized mix emerging from the orifice 107 of the extruder 10 the support.