Abstract: The invention concerns a method which consists in producing by radial expansion of the walls of two tubular parts (1, 2) engaged into each other substantially without play, in at least two zones of the parts spaced from each other in the axial direction of the parts (1, 2) two small protuberances (4) projecting radially outwards of the parts (1, 2) separated from each other, along the circumference of the parts (1, 2), by portions of the intermediate walls (5) of the parts. The small protuberances (4) are simultaneously produced in two zones spaced in the axial direction of the tubular parts (1, 2), using a tool comprising an expander with flexible blades on each of which are arranged two bosses spaced from each other in the expander axial direction. The invention is particularly useful for fixing an end sleeve (1) on a guide tube (2) of a fuel assembly.