Knurled Coupling for Z-Axis - fully parametrized

I am using stepper motors with 4mm shaft diameter, but most of the available z-axis couplings assume motors with a 5mm shaft. And since I also like to use the z-axis couplings as "knobs" to fine-tune manually the level and skewness of the z-coordinate, I like them to have a good tactile grip.

Since I couldn't find exactly what I had in mind among the many z-couplings available on Thingiverse, I ended up with my own *knurled* design.

The SCAD file is fully parametrized. Not just the d