Alfer Coaxis 27.5mm Corner Piece

I wanted to improve my printer by rebuilding it based on Aluminium Extrusions. As I never worked with them before I wanted to get a feel for them, so I went to my local hardware store and only found a system called "Coaxis" manufactured by Alfer. They have some positive sides, for example that you can just use m5 square nuts instead of special t-nuts and they're pretty cheap (8€/m). I decided to print my own connection pieces as the price for the original pieces from that manufacturer is pretty