A wheel hub bearing unit including an outer ring, rolling bodies and an inner ring provided with a flange at a first end thereof, the inner ring being made with a sliding surface for sealing lips of a sealing device arranged so as to protect the rolling bodies, defined by a metal insert formed integrally with the first end and arranged astride a base portion of the flange and a portion of the first end immediately adjacent to the base portion of the flange. The metal insert has a thickness of between 0.2 and 2 mm and being made, using a material different from the material with which the inner ring is manufactured and consisting of an austenitic stainless steel, by means of additive manufacturing.