Abstract: The invention relates to a fastener member for the production of assemblies, in particular a rivet. This fastener means includes a shank (1) and a head (2) intended to be deformed by flattening during installation. On its front face, this head has an annular groove (5) extending around the axis and positioned in proximity to the alignment of the exterior surface of the shank. This groove defines on the head two portions, one central (2C), the other peripheral (2P), able to be deformed independently under the effect of flattening. The invention enables a considerable improvement of the distribution of compressive forces between the fastener means and the materials to be assembled. It assures a satisfactory radial expansion of the head, as well as a sufficient flow of material toward the shank and the junction zone between shank and head.