Shelf brackets with French Cleat Mount

I needed some shelf space in my office, and I have been fascinated by French cleat mounting systems, so I came up with this simple design that provides a strong mount and hides the mounting screws.

I probably over engineered it with 6 walls and 25% infill. But it does seem sturdy and came out far better than I expected so I thought I'd share. I'm relativity new to CAD and 3D printing in general, l so I hope you like it. 

Edit: 12/22/2024

This is my first upload and it turned out nice for my needs but I'm sure it could be improved so I have changed the license to public domain and uploaded the step files. 

Edit: 01/09/2025 

Added multiple sizes from 3 1/2 “ to 9” with Step files.