A method for assembling a wheel hub bearing unit

Two rows of rolling elements (C1, C2) are arranged between an outer bearing ring (10) and a first inner ring (20) providing a cylindrical outer surface (27); a second inner ring (30), having a helical ridge (51) formed in an inner cylindrical surface (32), is rotated and advanced around and along the outer cylindrical surface (27) of the first inner ring (20), in such a way that the helical ridge (51) progressively carves a helical groove (52) in the cylindrical outer surface (27) of the first inner ring (20), until the second inner ring (30) reaches a locking position against one (C2) of the rows of rolling bodies, so as to exert a preload proportional to a tightening torque applied to the second inner ring (30) to lock it on the first inner ring (20).