Ever wonder what the numbers at the end of LuBest products mean? They are measurements of viscosity. Have you ever wondered what viscosity is? Viscosity is defined as oil’s resistance to flow. In the strictest sense, the units of kinematic viscosity are the Centistoke (cSt) (most common) and the Saybolt Universal Seconds (SUS) (almost obsolete). These systems describe the exact viscosity of an oil. What we generally see on products, though, is numbers that represent the product’s viscosity classification.
As the lubrication industry developed, different organizations and societies sprang up to help standardize oil classification. Each organization and society had their own ideas on how viscosity should be classified. The major ones that have survived are the Society of Automotive Engineers (SAE), the American Gear Manufacturer’s Association (AGMA), and the International Organization for Standardization (ISO). Each of these systems describes a range instead of an exact viscosity. In general, oils are tested at temperatures near their operating temperature.
The SAE system is perhaps the most familiar. It is the system used to describe viscosity of automotive motor oils and gear oils. It is generally tested at a temperature of 100°C (212°F) and is generally described as a weight, such as a 10 weight or a 90 weight oil.
The AGMA system was developed to describe industrial gear oils. It is tested at a temperature of 40°C (104°F). It uses a description system based on an easy numbering system, such as AGMA #8 oil.
The ISO system was developed as a way to describe oil viscosity across international borders. As industry has become more international, a way of describing an oil was needed so that everyone could understand and reference. In the United States, the ISO system is generally used to describe oils not covered by the above organizations, such as hydraulic, turbine, and slideway lubes. It is tested at 40°C.
At LuBest, we use all of the above classification systems to describe our lubricants. The system used for each oil “family” is the one most likely to be encountered in the field. For example, LuBest hydraulic oils follow the ISO system while LuBest industrial gear oils follow the AGMA system.
One system can be compared to another, however, if you compare the kinematic viscosity of the oil.
For example, an oil with a kinematic viscosity of 220 cSt @ 40°C would be equivalent to an SAE 50 Wt., an GMA #5, and an ISO 220.