Often when comparing greases NLGI numbers will be mentioned. What are these NLGI numbers?
In simple terms the NLGI is a measure of the relative hardness of a grease used for lubrication as determined by the National Lubricating Grease Institute (NLGI) in the USA. These standard classifications are widely used. The NLGI is a not-for-profit trade association that as part of its remit it publishes industry standards for greases.
Below is a useful table explaining NLGI numbers
(Reference: Rudnick, Leslie R. (2005). Synthetics, Mineral Oils, and Bio-Based Lubricants: Chemistry and Technology (Chemical Industries). CRC. p. 468. ISBN 1-57444-723-8).
|NLGI number||ASTM worked (60 strokes)
penetration at 25 °C
tenths of a millimetre
|Appearance||Consistency food analog|
|0||355-385||very soft||brown mustard|
|2||265-295||“normal” grease||peanut butter|
|4||175-205||very firm||frozen yogurt|
|6||85-115||very hard||cheddar cheese|
Common greases are in the range 1 through 3. Those with a NLGI No. of 000 to 1 are used in low viscosity applications. Grades 0, 1 and 2 are used in highly loaded gearing. Grades 1 through 4 are often used in rolling contact bearings. Greases with a higher number are firmer, tend to stay in place and are a good choice when leakage is a concern. For more information see Wikipedia.
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