Abstract: A lead screw with balls recirculating by deflector which has half-spherical supports with an undulating spheroidal movement for the self-alignment of the channel mouths of the nut-deflector unit is described. This is a deflector wherein the body (4.1) of the deflector has two equal half-spheres (4.3) adhered or joined laterally to it, each of the said half-spheres being joined to each of the walls (4.4) opposite to each of the entry mouths (9) of the S-shaped groove (7) of the deflector. The radius of the half-spheres (4.3) is equal to the radius of the ball bearings (1) and smaller than the generator radius of the semicircular profile of the channel (3.1) of the thread of the internal periphery of the nut. The distance between the body of the deflector and the points of contact (10) of the half-spheres with the canal of the nut is greater than the free play between the periphery of the deflector body and the walls of the housing hole (6).