Main heat sink for 1.67GHz (DL) model of the 15" Aluminium PowerBook G4. This unit will not fit the earlier versions of the PowerBook. This unit is thermally bonded to the processor and draws heat away. It is cooled by two fans which are mounted into the heat sink (fans sold seperately). Please be aware that a good thermal contact must be obtained with the processor if replacing this item. Thermal paste is available from the tools section.