the flanges 18 converge a layer of the material of bead 24 is squeezed or forced up into the seam formed between them this is a pumping or squeezing action that would occur even if the lower flange edges 12 were sharp but which is assisted by the slight chamfer as disclosed bead 24 is sufficiently thick that this squeezing action can occur if sufficiently thick this squeezed layer of flux and or flux and braze alloy can reach all the way to the top of the interface or seam between the abutted flanges 18 even acting to fill in the gap or trench at the top of the seam along tube outer surface o at the same time an ample supply of the original bead material remains between and to either side of the flange edges 12 if the flanges 18 were made with the l shape as disclosed in u s pat no 2 655 181 then the foot of the l would seat itself in the remaining bead material as the flanges 18 moved downwardly to their final folded position squeezing it out along tube inner surface i but still squeezing material up and into the seam while the converging motion of the faces of the flanges 18 occurs just from the folding down action a thinner layer of less viscous flux such as that which could be practically applied by a roller would not be sufficiently thick to enable bead material to be squeezed and forced up between the flanges once the final tube shape has been formed the next step is to cut the tube 26 to desired lengths and stack the tube lengths into a standard core such as a radiator or heater for example once stacked in a core.