a single tube 16 is shown in fig1 a swaging apparatus 18 including an elongated generally cylindrical drawbar 20 and a head 22 is inserted axially in the tube 16 from the primary side 12 of the tube sheet 10 as best shown in fig2 only a small annular clearance exists between the drawbar 22 and the tube 16 to permit insertion the drawbar 20 has a central section 24 that is encircled by three polyurethane pressurization rings 26 28 and 30 the intended pressure zone of the apparatus 18 being coextensive with these rings at each end of the pressure zone is a confinement structure 32 or 34 that positions the rings 26 28 and 30 the drawbar 22 includes separately formed annular shoulder members 36 and 38 by which the confinement means are prevented from moving axially toward the ends of the drawbar when swaging pressure is to be applied the drawbar 20 is retracted by a hydraulic piston not shown attached to the drawbar in the head 22 the rings 26 28 and 30 expand outwardly and the tube 16 is deformed radially outwardly the bore is then enlarged by deforming the tube 16 and the tube sheet 10 preferably the tube 16 exceeds its elastic limits but the tube sheet 10 does not so that the tube is permanently clamped in place where the swaging pressure is removed and the tube sheet 10 returns to its original shape due to the high swaging pressure the pressurization rings 26 and 30 at the ends of the pressure zone could be deformed inelastically and destructively into any void between the drawbar 22 and the tube 16 in the transitional areas.