a method and apparatus for manufacturing a centering , perfusion catheter balloon . a mold member is formed having an axial aperture . a plurality of axially spaced sets of transverse holes through the mold member . each set of holes includes one or more holes , with the holes in each succeeding set at a predetermined angle to the holes in the immediate preceding set . a tight fitting sleeve is provided around the mold member . a plastic tube is inserted into the axial hole and the assembly is heated and the tube is internally pressurized to cause the tube to expand the tube into the holes , forming outwardly extending knobs on the tube . the tube is cooled and fluid is evacuated from the tube , causing the tube to draw the knobs into the axial aperture to permit the completed tube to be withdrawn . the tube can then be assembled into a treatment catheter assembly with the knobs maintaining a treatment device centered in the balloon while the knobs allow fluid perfusion along the catheter .