I remixed https://www.printables.com/de/model/128980-lego-technic-beam-9x1 from https://www.printables.com/de/social/193542-kubikulak31 to create a piece that connects two studded Lego Technic beams vertically. This enables more rigid models.
Using this will probably get you expelled from Denmark for the rest of your life, so use at own risk.
Update: Version 2 looks better.
The author remixed this model.
I changed the spacing of the holes so it fits the pegs placed in two studded technic parts placed on top of each other.