I had some issues with the strength of the original Z nut lock (that resulted in vertical play) so I decided to design a stronger part.
I have done away with the anti-backlash nut and spring in favour of a "well" that tightly locks an M8 x 24mm coupling nut in place so it cant move in either direction. I've also added an extra (M3 x 12mm) screw to hold it all together securely.
I sourced my coupling nuts locally, but they are the same dimensions as these... https://www.fastenal.com/products/details/0161914
The trick is to use a flat screwdriver (or similar) to pry the end open so the coupling nut can be pushed in. (I then used my vice and a spare coupling nut to squeeze it all the way home).