CPV code 50221100 designates Repair and maintenance services of locomotive gearboxes in the Common Procurement Vocabulary (CPV 2008), the EU classification used to describe the subject of public contracts.
50221100 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).