A common confusion when looking on a turbocharger for the part number is the casting number. For example:
Garrett "M12" Turbo, "M12" being the raised lettering on the housing which is the casting number. The part number is usually located either on a stamped plate or on a flat surface on the turbocharger, sometimes the turbocharger may need to be wiped clean with a rag to make the part number location visible if covered in dirt and/or oil.
*Please note that from the casting we number we cannot know what the part number of the turbocharger is.