Tonneau cover corner braces
thingiverse
These are replacement inner and outer corners for a tri-fold tonneau cover. I don't know if these will work with other covers, but they fit snuggly with the stock aluminum extrusions. Hopefully they'll be useful for someone. I used fusion 360 to make the models. I'll put them up if anyone wants them.
Download Model from thingiverse
With this file you will be able to print Tonneau cover corner braces with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on Tonneau cover corner braces.