This is a bracket for making an EMT conduit shelf.

I have also attached the FreeCAD design so you can modify the design yourself.

Although, I used the Fasteners workbench so you may need to install that after installing the latest FreeCAD and going to Tools -> Addon Manager and searching for Fasteners.

I've gone through several iterations of the design.

The Mk V design uses a 25mm buttonhead M5 screw to create an expansion fitting that connects to the interior of a 1/2" EMT conduit using the two items marked as Part C and Part D.

Part B is missing as I've stopped using it since it was just a 7.5mm dowel that didn't hold the EMT snugly.

I printed these parts using 70% infill and the Ender 3's "dynamic" profile in Cura. I also attached a photo of what using lower infill looks like. The buttonhead M5 screw will pull out of the printed piece. So, use a higher infill for strength.

I was able to tighten the compression fitting and it held itself rigid for the most part which is pretty good considering it's only attached to the other length of EMT by a tiny bit of plastic at the end of the conduit. I wasn't able to pull the piece off at all once it was tightened.

Based on that, I'd say it's a successful joiner.