With balcony box holders specifically designed for balustrades with a round finish (preferably on closed balustrade walls, so that the boxes do not tilt forward due to gravity). The holders completely enclose the round material and fit tightly, as the adjustable openings can be adjusted to the profile diameter. The rubber strip on the inside does the rest for a secure hold - it also protects painted surfaces from scratching. Another detail: "storm protection" the manufacturer calls the sliding clamp hooks, which - pushed over the edge of the box - provide additional security in case of wind.