Bubble Lifter Boot - An off the shelf option.

Retail rubber boot ( Bubble Lifter )

Part #  9744K13
Price  $32.60
Phone  (330) 995-5500

It has a 1 13/16" I.D. at the top and a 3'' I.D. at the bottom. O.D.at the bottom is 4 1/2.
This boot will extend to 8'' and is 2'' when collapsed.
It has 9 ribs.

While not an exact match to the Robot's original, it is very close.