a are respectively provided in lateral radically outer regions of the stamping discs 10 11 and they interact with the inclined wall faces 1 a and form the desired structures there the structures are in this case the specially shaped flaps 3 described in the exemplary embodiments according to fig1 and 2 which also comprise a cutout in the inclined wall face 1 a with respect to the process of stamping such structures with a severe undercut by means of a longitudinal rolling method the stamping of the structures is at least usually easier and can take place in fewer steps the greater the incline of the wall face 1 a with respect to the perpendicular line of the plane of the fins in the exemplary embodiment according to fig1 and 2 approximately 10 u00b0 has been selected for such an angle w 3 which permits the flaps which are shaped in a complex way to be formed depending on the requirements and the shape and depth of the structures the angle can also preferably be between 10 u00b0 and 20 u00b0 in particular between 15 u00b0 and 20 u00b0 here a relatively large angle usually means a lower mechanical strength perpendicular to the plane of the fins for example action as a tie in the case of an internally corrugated fin of a charge air cooler and.