Before revision: The part design versus instantiations of it 400px|Parts marked with assined part numbers As a part number is an identifier of a part design (independent of its instantiations), a serial number is a unique identifier of a particular instantiation of that part design.
After revision: The part design versus instantiations of it 400px|Parts marked with assigned part numbers As a part number is an identifier of a part design (independent of its instantiations), a serial number is a unique identifier of a particular instantiation of that part design.