Strut Channel

Kindorf, Unistrut, SuperStrut, Metstrut, Strut Channel. It's the same stuff around the world.

In the US it's called:

1 5/8 x 1 5/8 square with 9/16 holes that are 1 7/8 inch apart

The rest of the world it's called:

41mm x 41mm with 14mm holes that are 47.5mm apart.

All built to the same international standard, managed at http://www.unistrut.org/

These are the solid files for HeeksCAD, and an STL. Great for making bots.