VISCOSITY- SAE, ISO or AGMA?

Oil viscosity is measured several ways. The three main ones that we encounter in equipment manuals are SAE, ISO, and AGMA. People are most familiar with SAE which stands for Society of Automotive Engineers. Engine oil viscosity is always measured in terms of SAE. Next we have the ISO system which stands for International Standardization Organization. The ISO scale is commonly used to measure the viscosity of industrial oils. Last but not least AGMA stands for American Gear Manufacturers Association. It can be confusing when you have a gear case that the manual says requires SAE 90 gear lube and one oil distributor gives you a pail that says AGMA 5 and another gives you a pail marked ISO 220. In terms of viscosity only, this is 3 ways of describing the same thing. In terms of viscosity they are equivilant. The chart below bears this out. The second dotted line goes horizontaly through ISO 220, AGMA 5, SAE 50 (engine), and SAE 90 (gear). Understanding the relationship of the viscosity scales to one another is useful but the viscosity of an oil is only part of what makes an oil a proper lubricant for a particular application. Other factors include the type of base oil and the additives with which the lubricant is formulated. Use the following chart to better understand the relationship of the viscosity measurement scales only. Please call for help to select an appropriate lubricant for your application.

 

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