OK, so this is yet another CR10 (SquashBall) vibration dampener foot. I use this not only to quiet down my CR10, but it helps reduce the impact of jerk allowing me to increase the print speed a bit more. It kind of feels like the printer is suspended in air, hence the name ;)
The squash balls (actually racquetballs) I used were 5.5cm or 2.17".
Printing it in PLA should be fine unless if you're using a heated enclosure, then maybe ABS would probably be best.
Didn’t need to use support, but would help to have the parts fan turned on.