These are components for an “extruded” framing system. There are 2 profile sizes, 15 x 15mm and 15 x 30mm. There are a few lengths of each. There are also 90 deg brackets and t-slot nuts for assembly. The t-slot nuts are designed for M3 screws (5 or 6mm long). Recommend printing a bunch of t-slot nuts The screen shots are just an example of the parts included and potential ways to connect them. It's a versatile way to create things to support/enclose your projects.
Print the extrusions vertically. Slow the print speed down for longer ones. If you don't want to have to take a file to the edges to get your t-slot nuts in, use rafts.
The author marked this model as their own original creation.