Abstract: A sheave block includes an internal ring, an external pulley wheel, which turns coaxially on the internal ring, rolling means set between the ring and the pulley wheel, and means of mutual axial retention of the ring and of the pulley wheel. The means of mutual axial retention have mutually facing integral races of the ring and of the pulley wheel in radial-axial contact with the rolling means. The internal ring has at least one angular area of localized increase of the radial distance between the integral races, where there is applied an insert for restoring said radial distance.