The document provides instructions and part numbers for a parts book covering a KX121-2 excavator. It lists various systems of the excavator including the basic engine, fuel system, cooling system, electrical system, hydraulic system, front attachments, track frame, swivel frame, operator's platform, and accessories. For each part, it provides the reference number, part number, description, quantity used, applicable serial number range, interchangeability, and remarks. It also provides notes about country codes that may be included in the parts book.