The invention relates to a bevel part for an insulating material and a sealing membrane, to be used with a screw and comprising a holding head (4) which is provided with an axial opening and is fixed to a tubular shank (5) ending coaxially to said opening. The shank (5) is generally cylindrical, receives the screw used, and has an inner diameter which is at least equal to that of the head of the screw. It has an end (6) which is pointed in such a way as to pierce a sealing membrane and to penetrate a thermal, phonic, or other, insulating layer. The pointed form of the shank (5) is shaped into a bevel and therefore has a bevelled surface bordered by two cutting edges (17a, 17b) converging towards a convergence point located on the end of the pointed form of the shank. The shank comprises a main projecting rib (13a) extending from the holding head (4) to the convergence point of the two edges (17a, 17b).