A remix of a quality bracket found on thingiverse.
It was scaled up 2.5%, and inner groves reduced. Proven to tightly fit Misumi 2020 #5 extrusions. If you want an even tighter fit, with a well-tuned printer you could print at 0.99 scale.
For use with M3 x 10mm bolts and M3 T-nuts. I also recommend using M4 washers on the side bolts - otherwise the bolts began to separate the vertical layers when tightened..
Recommend Print Settings:
2 layer shell, 1mm bottom/top, 30% infill.
Added v2. Now extends further down the Z axis, and the X/Y corner has been eliminated in order to attach cast aluminum braces in its place.