The invention relates to an insert (10) comprising a first end (12) defining a circular opening (14), a cylindrical body (16) having an inner wall (18) and an outer wall, and a second end (20) defining an opening (22) and forming an enlarged flange (24), characterized in that the body comprises a first portion (28) adjacent to the first end and provided with an outer thread (30), and a second portion (32) adjacent to the first portion and comprising at least two cutouts (34) defining at least two flexible tabs (36) extending axially, and each tab has an outer thread (38) and forms an angle (α), towards the outside of the body, with respect to the axis (A).Such an insert is used for axially positioning the outer rings of bearings.