Squash Ball Foot for CR-10 / Ender (or any 2040 extrusion)

To replace CR-10 feet with squash balls (double yellow dot), re-using existing M4 screws and T-nuts.

Also added a version for M3 screws if you're printing T-nuts. I did this on my Ender 3 since it didn't have hardware to re-use, you will need (16) M3 nuts and (16) M3x8mm bolts.

https://www.thingiverse.com/thing:2469130