Abstract: A rolling apparatus has a grooved roll rotatable about an axis, having an outer roll surface, and formed with a radially outwardly open groove having a pair of frustoconical groove flanks extending to the outer roll surface and spaced axially apart at the roll surface by a groove width. Juxtaposed with this grooved roll is a ridged roll rotatable about an axis parallel to the axis of the grooved roll and formed with a ridge engaging radially in the groove, and having an at least partially cylindrical outer ridge surface centered on the respective axis and a pair of annular axially oppositely directed ridge faces flanking the ridge outer surface. The ridge outer surface forms with the flanks of the groove a rolling opening extending perpendicular to a plane including the axes and having a maximum dimension measured parallel to the axes which is smaller than the groove width.