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 |
|---|---|---|---|
| 000 | 445-475 | fluid | cooking oil |
| 00 | 400-430 | semi-fluid | apple sauce |
| 0 | 355-385 | very soft | brown mustard |
| 1 | 310-340 | soft | tomato paste |
| 2 | 265-295 | “normal” grease | peanut butter |
| 3 | 220-250 | firm | vegetable shortening |
| 4 | 175-205 | very firm | frozen yogurt |
| 5 | 130-160 | hard | smooth pate |
| 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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