This SAE Recommended Practice has been formulated to advance and endorse the use of the ISO (International Organization for Standardization) Solid Contaminant Code as the universal means for expressing the level of particulate contaminant in hydraulic fluid and for specifying acceptable limits of cleanliness. Worldwide approval was gained for this coding system because it provides a simple, unmistakable, meaningful, and consistent means of communication between suppliers and users. The code applies to all types of hydraulic (liquid) fluids used in fluid power and control systems.