A method during which is produced, in an outer wall of a tube extending along a longitudinal axis, through guiding punches in a working plane and in a working direction concurrent with the longitudinal axis of the tube, at least one notch (11, 12, 13, 13a, 13b) comprising at least one locking flank, in which method the following steps are performed: • ST1: a first punch is guided in the working direction, a preforming tooth of the first punch extending from one end of the first punch and parallel to the working plane, an intersection of a leading end of the preforming tooth with the working plane forming a straight line, and an intersection of said leading end of the preforming tooth with a plane parallel to the longitudinal axis of the tube forming a convex curve, and onto the first punch is exerted a preforming force capable of causing the preforming tooth to penetrate into the wall of the tube until obtaining a protuberance (55, 56) of material on both sides of the leading end of the preforming tooth, a solid cylindrical mandrel being positioned inside the tube, then • ST2: a second punch (70, 80) is guided in the working direction, a punching tooth (72, 82) of the second punch extending from one end (71, 81) of the second punch and parallel to the working plane, a leading end (73, 83) of the punching tooth (72, 82) having a shape complementary to a shape of the notch to be produced, and on the punch and is exerted a punching force capable of causing the punching tooth to penetrate into the wall of the tube by a radial distance equal to the depth of the notch to be produced, a punching mandrel being positioned inside the tube, said punching mandrel having, near to a notching area, a groove adapted for containing a material displaced during the displacement of the second punch. • ST1: a first punch is guided in the working direction, a preforming tooth of the first punch extending from one end of the first punch and parallel to the working plane, an intersection of a leading end of the preforming tooth with the working plane forming a straight line, and an intersection of said leading end of the preforming tooth with a plane parallel to the longitudinal axis of the tube forming a convex curve, and onto the first punch is exerted a preforming force capable of causing the preforming tooth to penetrate into the wall of the tube until obtaining a protuberance (55, 56) of material on both sides of the leading end of the preforming tooth, a solid cylindrical mandrel being positioned inside the tube, then • ST2: a second punch (70, 80) is guided in the working direction, a punching tooth (72, 82) of the second punch extending from one end (71, 81) of the second punch and parallel to the working plane, a leading end (73, 83) of the punching tooth (72, 82) having a shape complementary to a shape of the notch to be produced, and on the punch and is exerted a punching force capable of causing the punching tooth to penetrate into the wall of the tube by a radial distance equal to the depth of the notch to be produced, a punching mandrel being positioned inside the tube, said punching mandrel having, near to a notching area, a groove adapted for containing a material displaced during the displacement of the second punch.