Grease Viscosity and NLGI Number Grades

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	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

The worked penetration values in the table are determined by the ASTM (American Society for Testing and Materials) testing methods. ASTM D 217 and D1403 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.

The test methods provide different results for "worked" and "unworked" grease. Handling or working a grease tends to soften it a bit, resulting in a higher penetration number. Since any grease that is delivered through an automated greasing system is definately worked, we have provided only worked values here.Data sheets, available from grease manufacturers usually provide the worked and unworked penetration values, along with the NLGI grade.