Original Creator bigbrisco on thangs, I adapted it to FreeCAD.
The model parameters can be adjusted via the dimension variable spreadsheet to make whatever size you want.
Update: Check out my new FreeCAD Gridfinity Workbench for many more options and features: https://github.com/Stu142/FreeCAD-Gridfinity-Workbench
The author remixed this model.
FreeCAD version of the model created by the original create.