I was fedup when I printed another Z stop I found on thingiverse. The silly thing was way oversized and the M2 octagonal knob just slipped. Waste of material and time!
So I made my own. It's strong and chunky and will last you a lifetime. And it fits properly on the original M2 octagonal knob. To ensure it will fit make sure it's a max of 33mm between flats on the original M2 knob.
You can also flip it over and use it as a winding handle. But dont leave it on when printing, as it will interfere if the extruder gets close.
I printed mine in PLA at 0.2mm with 15% infill. But you can pretty much choose whatever you like.