HP Top Cover 821155-001 is a replacement cover for the HP ZBook 15u mobile workstation. HP’s service documentation identifies this exact spare part for ZBook 15u models, including the G3 and G4 generations.
The top cover is one of the computer’s main parts, removed during servicing after the other components have been taken out. It is intended for replacing that specific cover as part of a ZBook 15u repair.
HP’s documented procedure reverses the removal steps to install the cover. The part number distinguishes it from the top covers listed for other notebook models.