Abstract: A tubular compact (14) obtained by compacting a powder is applied with one circumferential surface (16) at a minimum distance required for said application, from an abutment surface (15) corresponding to said one circumferential surface (16). The space between said one circumferential surface (16) and the abutment surface (15) is evacuated, such that the compact (14), while undergoing a certain deformation to bridge said space, is sucked against the abutment surface (15) so as to be firmly retained against it.