Campagnolo rear derailleur cage pivot mounting sleeve/h screw worm gear RD-PO004. It allows the top jockey wheel to cassette distance to be fine tuned.
This part is used on all Campagnolo rear derailleurs 9, 10, 11 and 12 speed.
Fits Super Record, Record, Chorus, Potenza, Athena, Centaur, Veloce and Mirage.
The H screw is available as a spare in the complete cage which is specific to the rear derailleur.