I mixed the feet used in a CR-10s project, I used the claw bit for the ball and redesigned the base.
I designed this to fit 45mm squash balls, these are not "standard" squash balls and instead they are called Dunlop INTRO squash balls.
They are bouncier than a standard squash ball hence why I chose them to give better dampening properties.
I bought them form amazon UK, here is the link.
DUNLOP Intro Pack of 3 balls https://www.amazon.co.uk/dp/B00J04SP36/ref=cm_sw_r_cp_api_i_wDoQDb8B88VTQ
There is no need for any hardware to attach them, just place them under your existing feet and pop a ball in!
Once they are all on the printer does wobble a bit when you touch it. (i.e. for loading filament and removing things from the bed) but it is steady during printing as the effector is not heavy enough to move the machine.
I have initially printed in PLA as I haven't sorted an enclosure yet but I will print in ABS eventually.
Oh, and I know the claw is not perfectly round! It took lots of effort to resize to 45mm and I lost the will by the time I got them to this point! It does not affect how they work :-)
30% on PLA - Probably less on ABS
Printed at 80mm/s
Took approximately 4 hours per foot, you need 3
If you use support it will be in foot holes, it should snap out easily, I printed on with support and 2 without (by accident) it bridged the hole ok.