By Lukeron Lubricants · Last updated
Quick answer
NLGI is a number that shows how stiff a grease is. NLGI 2 is the standard grade for most bearings, wheel hubs and general greasing. NLGI 0 and 1 are softer, for centralized systems and for cold or slow applications. NLGI 3 is firmer, for high-speed, hot or sealed bearings. A higher number means a stiffer grease, not a better one. Always use the grade in the machine maker's manual.
NLGI grade chart
| NLGI grade | Feel | Penetration (0.1 mm) | Typically used for |
|---|---|---|---|
| NLGI 000 and 00 | Fluid | 400 to 475 | Gearboxes and centralized systems that need a very fluid grease |
| NLGI 0 | Semi-fluid | 355 to 385 | Centralized lubrication systems, slow-speed gear cases |
| NLGI 1 | Soft | 310 to 340 | Cold conditions, large slow bearings, some centralized systems |
| NLGI 2 | Medium | 265 to 295 | General purpose: ball and roller bearings, wheel bearings, chassis, electric motors |
| NLGI 3 | Firm | 220 to 250 | High-speed, hot or sealed bearings, where the grease must stay in place |
| NLGI 4 to 6 | Very stiff | 85 to 205 | Rare. Special uses only |
Penetration is the standard worked penetration at 25 C (ASTM D217): a lower number means a stiffer grease. The uses shown are typical. Follow the machine maker's manual.
Grease is one of the most misunderstood lubricants in industrial and automotive maintenance. Many maintenance technicians default to NLGI 2 for everything — a reasonable starting point, but not always correct. Choosing the wrong grease consistency can lead to bearing failures, pump blockages, or grease purging from housings in ways that reduce lubrication effectiveness.
What Is NLGI Consistency Grade?
NLGI stands for National Lubricating Grease Institute, and the consistency grade is a standardized measure of how stiff or fluid a grease is. The scale runs from NLGI 000 (very fluid, almost like an oil) to NLGI 6 (very stiff, brick-like). The test used is the cone penetration test — a standardized cone is dropped into the grease and the depth of penetration in tenths of a millimeter is measured. Higher penetration (softer grease) = lower NLGI grade.
NLGI 0 and 00: Semi-Fluid Greases
NLGI 00 and 0 greases are nearly fluid at room temperature and flow under gravity. They are used in centralized lubrication systems where fluid flow through lines and fittings is required, gear cases where a fluid lubricant is needed but an oil circulation system is not practical, and industrial gearboxes with slow rotation where fluid grease provides better coverage.
NLGI 1: Soft Grease for Cold and Low-Speed Applications
NLGI 1 is softer than standard bearing grease and is used for: low-temperature applications where stiffer grease would not flow adequately to lubricate bearing surfaces, large slow-speed bearings where good coverage requires the grease to flow across the bearing surface, and some centralized lubrication systems where NLGI 2 proves too stiff to pump reliably.
NLGI 2: The Universal Standard
NLGI 2 is the most widely used grease consistency in industrial, automotive, and marine applications. It strikes the balance between stiffness (stays in place in bearing housings) and softness (can be pumped through grease guns and centralized systems, and penetrates bearing cages adequately). Ball bearings, roller bearings, automotive wheel bearings, electric motor bearings, and most general-purpose applications use NLGI 2.
When NLGI 2 is the right choice
- Ball and roller bearings, wheel bearings, electric motor bearings and chassis points that the machine maker lists for a general-purpose grease.
- Places where the grease is applied with a hand grease gun or a line that pumps NLGI 2 easily.
- Ordinary temperatures and speeds, where the grease has to stay in the housing and still reach the bearing.
When NLGI 2 is not the right choice
- Centralized systems and cold conditions often need a softer grease, NLGI 0 or NLGI 1.
- High-speed, hot or sealed bearings often need a firmer grease, NLGI 3.
- If the machine maker names a grade, use it. NLGI 2 is a common starting point, not a rule.
NLGI 2 describes stiffness, not the type of grease
Two NLGI 2 greases can behave very differently. NLGI 2 only says how stiff the grease is. The thickener and the base oil decide the rest, such as the drop point (the temperature at which a grease starts to melt), water resistance and load capacity. For example, Lukeron's EPL-2 grease is NLGI 2 with a drop point of 175 to 185 °C, while the Lukeron calcium sulfonate grease is NLGI 2 with a drop point of 250 °C and above.
Many Lukeron industrial greases, including lithium complex, EP, high-temperature non-melt, calcium graphite and calcium gel greases, are made in all four grades from NLGI 0 to 3, so the same grease can be supplied in NLGI 2. Lukeron also makes NLGI 2 spindle grease for high-speed spindles and NLGI 2 power tools grease.
NLGI 3: For High-Speed, High-Temperature, and Sealed Applications
NLGI 3 is stiffer than standard bearing grease and is preferred for: high-speed bearings where fluid grease would be centrifuged out or churned excessively, sealed-for-life bearings where the grease must remain in place without replenishment, high-temperature applications (kiln bearings, oven conveyors) where the grease must resist softening, and electric motors in hot environments where grease leakage onto windings must be prevented.
Base Oil Type in Grease Also Matters
Beyond NLGI grade, the base oil in the grease matters for temperature range and compatibility. Lithium complex greases provide high temperature performance (dropping point above 250°C) and are widely used. Calcium sulphonate greases offer excellent water resistance and are preferred in marine and wet environments. Polyurea greases are used in sealed-for-life bearings. PTFE (Teflon) greases are food grade compatible and used in light-load, clean environments.
Lukeron makes greases in NLGI grades 0, 1, 2 and 3. See the greases by grade below, or ask our team for a quote and data sheets.