Aluminium tube "placeholder"

I need to do a "physical simulation" before cut the 20mm square aluminium bars, so I create a customizable printable structure, this can be useful in other situations too.
Easy and relatively cheap to print: https://youtu.be/JCrF-TCE00w
Two STL provided: 50mm and 150mm length, use customizer or the scad file provided to adjust it according your needed.