I designed this to take a bowden fitting that has an M6 thread (the Fusion 360 files are attached if you need something different). The threads weren't perfect when I printed them, but they clean up nicely with an M6 tap. It attaches to the uprights with the #6 x 5/8" (16mm) Thread Forming Screws described in the RepRack repo.
The author remixed this model.
New crossmember design to attach a bowden fitting.