Abstract: In a square cover plate, a one-piece folding blank has a square cutaway that is rotated by 45° relative to the square shape of the cover plate. This square cutaway is arranged concentrically to a convex, octagonal groove-line and scoring-line structure. In this case, groove lines and scoring lines alternate respectively in such a way that the scoring lines wind up parallel to the outside edges of the cover plate, and the groove lines wind up parallel to the outside edges of the square cutaway. From the center of the scoring lines, in each case perpendicular to the scoring line, a flap separation cut up to the respective corner of the inside square cutaway is inserted into the cover plate. As an alternative, a flap main separation cut is inserted in the direction of the center of the respectively opposite scoring line and perpendicular to this scoring line in the cover plate from the respective corner of the inside square cutaway.