The correct answer is C. 3 parts . ISO 4406 fluid cleanliness coding is used in oil and hydraulic-fluid analysis to classify particulate contamination. The code is normally shown as three numbers, such as 18/16/13 or 19/17/14. Each number represents a particle-count range for a specific particle-size threshold. The common ISO 4406 reporting sizes are particles greater than 4 µm, greater than 6 µm, and greater than 14 µm. Option A is wrong because two parts would omit one of the required particle-size channels. Option B is wrong because four parts is not the standard ISO 4406 code structure. In the CRL Asset Condition Management domain, fluid cleanliness matters because particulate contamination is a major cause of hydraulic, lubrication, bearing, valve, and servo-system failure. Understanding the three-part code allows reliability leaders to set cleanliness targets, evaluate filtration performance, and detect contamination-driven degradation before functional failure occurs. ISO 4406 references three particle-size counts, confirming the answer.