To obtain a connection between a foldable sheet material member and a suspension or stiffening member said sheet material member is first provided with a longitudinal bead having a wider upper portion and a narrower lower portion, whereupon the bead is sideways introduced in a corresponding downwardly open groove in the suspension or stiffening member. The bead is made by folding the sheet material along a plurality of folding lines, located in near vicinity to each other, at least some of said folding lines being made by punching in the sheet material a plurality of elongated slots, leaving between two adjacent slots a relatively long unpunched portion thus obtaining an easily foldable fold, difficult to tear. By varying the foldability of the folds for example by varying the length of the slots complicated foldings may be easily obtained in automatic processes.