It used to be the practice to define the viscosity of industrial lubricating oils in Saybolt Universal Seconds (SUS) at reference temperatures of 100OF and 210°F. However, there is now world-wide acceptance of the International Organization for Standardization's (ISO) system for viscosity measurement in centistokes (cSt) at 400C and 100°C.
International acceptance benefits customers, manufacturers and marketers.
The lubricant grade recommended by the equipment manufacturer is the same as the number in the product name.
Conversion from one viscosity measurement to another is virtually eliminated.
The number in the product name for most products represents the viscosity of an industrial oil. Automotive engine and gear oils are not involved in the ISO measurement system. They continue to be described by the Society of Automotive Engineers (SAE) viscosity classifications. The table below shows the kinematic viscosity limits for each ISO Viscosity Grade. Each << viscosity grade is 50% higher in viscosity than the preceding viscosity grade. These limits are set at a 10 percent tolerance level above and below the mid-point of a grade. Any product with a viscosity outside these tolerance levels is not a recognized ISO Viscosity Grade.