The National Association of Lubricating Grease Manufacturers, Inc. (NLGI) is a not-for-profit association composed of companies who primarily manufacture and market various types of lubricating grease. The objectives of the NLGI are to disseminate information that can lead to the development of better lubricating greases for the consumer and to provide better grease lubrication engineering service to the industry.

The NLGI consistency number expresses a measure of the relative hardness of a grease used for lubrication, but is only one factor in determining suitability of a grease to a specific application. The consistency of grease (its ability to resist deformation by an applied force)  is controlled by the thickener concentration, thickener type and the viscosity of the base oil.  NLGI’s classification defines nine grades, as shown below; each correlated to a range of ASTM worked penetration values, measured using two test apparatus. The first apparatus consists of a closed container and piston-like plunger that is perforated to allow grease to flow from one side to the other as the plunger is moved up and down.  The test grease, with a constant temperature of 25 degrees Celsius,  is inserted into the container and stroked 60 times before being moved to a penetration test apparatus. This apparatus consists of a container, specially configured cone and dial indicator that, once filled,  is smoothed over. With the cone’s tip touching the grease’s surface and the dial indicator set to zero, the test begins. Over a specified period of time, the weight of the cone will cause it to penetrate the grease, after which time, the depth of penetration is measured.

• NLGI Grade 000 – Extremely Fluid (similar to cooking oil)/ Worked Penetration in Tenths of a Millimeter: 445-475
• NLGI Grade 00 – Fluid (similar to applesauce)/Worked Penetration in Tenths of a Millimeter: 400-430
• NLGI Grade 0 – Semi-Fluid (similar to brown mustard)/Worked Penetration in Tenths of a Millimeter: 355-385
• NLGI Grade 1 – Very Soft (similar to tomato paste)/Worked Penetration in Tenths of a Millimeter: 310-340
• NLGI Grade 2 – Moderately Soft (similar to peanut butter)/Worked Penetration in Tenths of a Millimeter: 265-295
• NLGI Grade 3 – Semi- Solid (similar to vegetable shortening)/Worked Penetration in Tenths of a Millimeter: 220-250
• NLGI Grade 4 – Medium-Solid (similar to frozen yogurt)/Worked Penetration in Tenths of a Millimeter: 175-205
• NLGI Grade 5 – Hard (similar to a smooth pate)/Worked Penetration in Tenths of a Millimeter: 130-160
• NLGI Grade 6 – Very Hard (similar to cheddar cheese)/Worked Penetration in Tenths of a Millimeter: 80-115

High consistency greases, as indicated by  higher NLGI numbers, are recommended for use in high ambient or operating temperatures when bleeds or leaks are of concern. These greases are firmer and tend to stay in place and may be used on high-speed ball/roller bearings, with low-viscosity base oil, or on low-speed journal bearings. Lubricants with a lower consistency, or NLGI number, are suggested for cold temperature operations on low-speed rolling element bearings, with high viscosity. A common mistake when selecting a grease is to confuse the grease consistency with the base oil viscosity. It’s important to remember that that both speed and load help determine the appropriate viscosity required for application. Even though base oil viscosity affects consistency, it is possible for a grease to have a high consistency and low base oil viscosity or vice versa.

Companies, such as Schaeffer Oil are helping make NLGI consistency identification simple through the use of color-coded caps on their high-temperature, waterproof, synthetic and high- pressure greases. Available in a variety of grades to suite the unique application requirements of its users,  Schaeffer Lubricants feature black, white, red, yellow and clear tops that correlate directly to NLGI consistency numbers. Understanding these differences and knowing which cap to look for, will help make choosing the right grease look easy.

NLGI #00 – Schaeffer Black Cap

NLGI #0 – Schaeffer White Cap

NLGI #1 – Schaeffer Red Cap

NLGI #2 – Schaeffer Yellow Cap

NLGI #3 – Schaeffer Clear Cap