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That's 98613c01 - Hero Factory Arm / Leg Extender with Ball Joint and Ball Socket on BrickLink.
LEGO call this item Ball Cup High Friction W. Rubber and use 74261 (design ID) and 6106472 (Element number) for latest sets.
LEGO doesn't always have full list of parts within a set as this depends on parts availability (maybe some other reasons too). You would ...
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