Consistency, Penetration, and National Lubricating Grease Institute (NLGI) Numbers

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Consistency, Penetration, and National Lubricating Grease Institute (NLGI) Numbers

Consistency, penetration, and National Lubricating Grease Institute (NLGI) numbers: The most important feature of a grease is its rigidity or consistency. A grease that is too stiff may not feed into areas requiring lubrication, while a grease that is too fluid may leak out. Grease consistency depends on the type and amount of thickener used and the viscosity of its base oil. A greases consistency is its resistance to deformation by an applied force. The measure of consistency is called penetration. Penetration depends on whether the consistency has been altered by handling or working. ASTM D 217 and D 1403 methods measure penetration of unworked and worked greases. To measure penetration, a cone of given weight is allowed to sink into a grease for 5 seconds at a standard temperature of 25C (77F). The depth, in tenths of a millimeter, to which the cone sinks into the grease is the penetration. A penetration of 100 would represent a solid grease while one of 450 would be semifluid. The NLGI has established consistency numbers or grade numbers, ranging from 000 to 6, corresponding to specified ranges of penetration numbers. Table A, below lists the NLGI grease classifications along with a description of the consistency of each classification.

Table A

NLGI Grease Classification Table Chart
NLGI Number ASTM Worked Penetration
0.1 mm (3.28 10 ft) at 
25C (77F)
0000 445 - 475 Semifluid
00 400 - 430 Semifluid
0 355 - 385 Very soft
1 310 - 340 Soft
2 265 - 295 Common grease
3 220 - 250 Semihard
4 175 - 205 Hard
5 130 - 160 Very hard
6 85 - 115 Solid

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