Update 20/3/2024 - I've added a new connector that you can push in from the side, like the GPro Walls.  The clip is smaller and will allow a wall to placed above it, on stacked columns.  Thanks again to the Masked Marble for suggestions for improvement.

After feedback on Girders and braces, a model I published earlier. It became clear that sizing the girders accurately was a significant issue. I'm still working on getting the sizing right, however a couple of comments from the Masked Marble, pushed my thinking in a different direction. Instead of having fixed by flexible girders, a rigid but adjustable approach might be better. So after much trial and error, G-Beam in three different sizes, provides a means to fit support structures into Pro pillars and allow you the builder to adjust the fit.

Each beam is composed of 2 connectors and a hollow T beam. The connectors are wiggled into the voids at the end of the beam. They are a tight fit, they will become easier to fit with wear. There's a close up photo to show which way up the connector should be inserted. The beam is inserted into the pillars with flat part of the T facing up.

Here's a short video of how to construct a G-Beam.