Hello Hedi

> I've check again but I don't think that U-profil 20 x 20 mm with 1 mm thickness exist.

You are assumingly right, I found a U-profile 20mm height and 19mm base
width at http://www.aluminium-profile.org/aluprofile/uprofil/uprofile.php
model UP2019201
and 20x20 but 1,5 mm thickness
UP2020201.5

Florian