The aluminium strip foot section is first formed into an L shape and then tension wrapped on to the base tube. Wound fin base sections are close to each other so as ensure a continuous cover over the primary tube surface. Finally, the fin strip is fastened at ends to prevent loosening.

An aluminum strip is folded to form an L shape and then wound around the base tube. The feet of the fins are joined together and covers the whole of the tube surface. The root of the fin is simultaneously knurled with the inner tube ensuring tight contact between fins and tube.

Fin consists of an aluminium strip whose foot edge is tension wrapped and embedded into the primary tube wall.

A core tube, or liner is fitted into an aluminium primary tube. This tube-in-tube assembly is then fed into the finning machine equipped with three spindles. The gang discs which are stepped in profile and diameter will first extrude and shape the fin properly and then shrink fit the primary tube on its liner.