Oil Classifications and Grading Systems

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Oil Classifications and Grading Systems

Professional societies classify oils by viscosity ranges or grades. The most common systems are those of the SAE (Society of Automotive Engineers), the AGMA (American Gear Manufacturers Association), the ISO (International Standards Organization), and the ASTM (American Society for Testing and Materials). Other systems are used in special circumstances.

The variety of grading systems used in the lubrication industry can be confusing. A specification giving the type of oil to be used might identify an oil in terms of its AGMA grade, for example, but an oil producer may give the viscosity in terms of cSt or SUS. Conversion charts between the various grading systems are readily available from lubricant suppliers. Conversion between cSt and SUS viscosities at standard temperatures can also be obtained from ASTM D 2161.