Multi-spindle operating head comprising a central structure adapted to rotate orthogonally to a work plane, said central structure supporting a plurality of electro spindles distributed on a circumference with the same angular distance, the rotation axis of each electro spindle disposed radially with respect to the axis of rotation of the central structure , the central structure comprising a seat adapted to receive each electro spindle by means of a mechanical interface in order to arrange at least an array of rings (r3), (r4) aligned on at least one circumference (D3), (D4) coaxial with the central structure , characterised in that : - each of said plurality of electro spindles connected to the multi-spindle operating head comprises a cylindrical casing longitudinally delimited by a front flange and a rear flange , a shaft rotatably supported by both the front flange and the rear flange by means of bearings, an interface flange , a rotor attached to the shaft, a stator attached to an inner wall surface of the cylindrical casing so as to surround the rotor, an electrical connector mounted on the rear flange and electrically connected to the stator, the cylindrical casing consisting of a first section (t1) to support the interface flange through the front flange and a second section (t2) provided with said mechanical interface to connect the electro spindle to the multi-spindle operating head, said first section (t1) surmounted by at least one of the two rings (r3), (r4), said two rings (r3), (r4) positioned so as to form a first U-shaped transverse annular channel (c34) and a second U-shaped transverse annular channel (c4); - the surface of the first section (t1) is approximately increased by at least twice through the rings (r3), (r4) and the channels (c34), (c4); - the thickness of each ring (r3), (r4) is approximately equal to the thickness of the front flange or to that of the rear flange . - each of said plurality of electro spindles connected to the multi-spindle operating head comprises a cylindrical casing longitudinally delimited by a front flange and a rear flange , a shaft rotatably supported by both the front flange and the rear flange by means of bearings, an interface flange , a rotor attached to the shaft, a stator attached to an inner wall surface of the cylindrical casing so as to surround the rotor, an electrical connector mounted on the rear flange and electrically connected to the stator, the cylindrical casing consisting of a first section (t1) to support the interface flange through the front flange and a second section (t2) provided with said mechanical interface to connect the electro spindle to the multi-spindle operating head, said first section (t1) surmounted by at least one of the two rings (r3), (r4), said two rings (r3), (r4) positioned so as to form a first U-shaped transverse annular channel (c34) and a second U-shaped transverse annular channel (c4); - the surface of the first section (t1) is approximately increased by at least twice through the rings (r3), (r4) and the channels (c34), (c4); - the thickness of each ring (r3), (r4) is approximately equal to the thickness of the front flange or to that of the rear flange . <EOS>