Abstract: A pair of facing die sections, preferably constructed of machinable plastic, are biased toward one another and their central regions are spaced to form a shallow gap. Each die section is provided with a tapered folding chamber whose wide end is open at the upstream end of the die section. Each chamber communicates with the gap by means of a shallow slot that extends longitudinally, or in the direction of travel of a tape that is drawn through the gap. The edges of the tape enter the folding chambers as the central main section of the tape enters the upstream end of the gap. While the tape edges are in the chamber they are curled and directed through the slots into the gap. By the time the edges leave the chambers these edges are folded to lie flat against opposite sides of the main section of tape. Means are provided for adjusting the die sections to operate on different widths of tape and to produce desired widths for the folded edges.