CPV code 50221200 designates Repair and maintenance services of locomotive transmissions in the Common Procurement Vocabulary (CPV 2008), the EU classification used to describe the subject of public contracts.
50221200 is a leaf code — the most specific level of its branch — so it can be used directly as the main CPV code of a contract notice. If it does not quite fit, check the neighbouring codes under 50221000 (Repair and maintenance services of locomotives).