is simplified system established by the National Lubricating Grease Institute (NLGI) for rating the consistency of grease.  The ability of any particular grease to be handled by grease pumps, grease dispensers, and other components in a automated greasing system depends on the grease viscosity (thickness). Grease is a mixture consisting of a natural or synthetic oil base combined with thickeners and additives. Grease viscosity depends on the amount and type of thickener(s) used as well as the viscosity of the base oil. The NLGI (National Grease Lubricating Institute) has established a scale of 000 to 6 representing very low to very high viscosity.

NLGI Grease Classification
NLGI Grade	ASTM Worked Penetration at 25°C (77°F)	Consistency
000	445 - 475	Semi-fluid
00	400 - 430	Semi-fluid
0	355 - 385	Very Soft
1	310 - 340	Soft
2	265 - 295	Common Grease
3	220 - 250	Semi-Hard
4	175 - 205	Hard
5	130 - 160	Very Hard
6	85 - 115	Solid

Worked penetration values in the table are determined by the ASTM (American Society for Testing and Materials) testing methods. ASTM-D-217 and D-1403 are described as "Standard Test Methods for Cone Penetration of Lubricating Grease". To measure penetration, a cone of given material, weight, and finish is allowed to sink into a grease for 5 seconds at a standard temperature of 25°C (77°F). The depth, in tenths of a millimeter, to which the cone sinks into the grease is the penetration

Also see penetration (grease).