Was one of my first upgrades with a little adaption of the original model so that it fit's to Neptune 3. It makes such a big difference to the standard feets so that I would recommend it to everybody as must have.
Maybe also for the newer Neptune 4, but I don't know. Maybe someone will check and confirm.
You can use standard Squash Balls and use the original bolts from the standard feet.
Print is very easy, no supports needed.
The author remixed this model.
Adaption to Neptune 3 Pro Model