A coordinate positioning apparatus for inspecting an artefact. The coordinate positioning apparatus includes at least one moveable member moveable in at least one degree of freedom, and at least one motor and at least one bearing arrangement for facilitating said movement. At least a part of the at least one motor and/or at least one bearing arrangement are located inside a protective housing therefor. A ferromagnetic contamination trap comprising at least one magnet is provided and configured to attract and retain ferromagnetic contamination entering the protective housing.