CPV code 42124310 designates Parts of air pumps in the Common Procurement Vocabulary (CPV 2008), the EU classification used to describe the subject of public contracts.
42124310 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 42124300 (Parts of air or vacuum pumps, of air or gas compressors).