The device comprises two L-shaped angle profiles with fixture arms under 1.5mm thick and having breakthroughs. The fixture arms have closure arms (12) joined to one another by a bridge profile (2) of plastics approximately U-shaped in cross-section. The arms are inserted and supported in pockets on the outside of the closure arms of the angle profiles. The bridge profile has a softly adjusted stay (21) and on its underside has a hard adjusted arm (22), whereby the softly adjusted elastic stay locates with its lateral limitations (211) with tension in a sprung fashion on the outsides (121) of the closure arms. The side walls forming the lateral limitations of the stay are inclined to the vertical and locate on corresp. inclined surfaces (121) of the outside of the closure arms.
