This is a simple corner bracket for strengthening corner joints in 2020 extrusion structures. This is designed with 3D printers in mind, but if you have 2 pieces of 2020 extrusion meeting at a 90-degree angle, this can help. 

I have only tested this with Misumi brand extrusion but I suspect this will work with just about any version of 2020 extrusion. 

I printed mine out of ABS+ but you can use whatever material that meets your needs.