NLGI Grease Grades
National Lubricating Grease Institute consistency grades for grease classification based on worked penetration testing according to ASTM D217.
The NLGI grade system classifies greases by consistency (stiffness) based on a standardized cone penetration test. This is the most widely used grease classification system worldwide.
Understanding the Penetration Test
The worked penetration test (ASTM D217) measures how far a standard cone sinks into the grease under specified conditions:
- Grease is “worked” 60 double strokes to simulate handling
- Cone is released and allowed to sink for 5 seconds
- Penetration depth is measured in tenths of a millimeter
Higher penetration numbers indicate softer grease.
Grade Selection Factors
Speed
Higher speeds generally require softer greases (lower NLGI grade) to reduce churning resistance and heat generation.
Temperature
Higher operating temperatures require firmer greases (higher NLGI grade) to maintain consistency. Consider both ambient and operating temperatures.
Sealing
Vertical shafts and applications exposed to water or contaminants may benefit from firmer greases that resist leakage.
Dispensing Method
Centralized lubrication systems require softer greases (NLGI 0-1) that can flow through tubing.
Limitations of NLGI Grade
The NLGI grade tells you nothing about:
- Base oil type or viscosity
- Thickener type
- Additive package
- Temperature range
- Load-carrying capacity
- Water resistance
Two greases with the same NLGI grade may have completely different performance characteristics.
Classification Table
| NLGI Grade | Worked Penetration (0.1mm) | Consistency | Common Comparison |
|---|---|---|---|
| 000 | 445-475 | Very fluid | Cooking oil |
| 00 | 400-430 | Fluid | Applesauce |
| 0 | 355-385 | Semi-fluid | Brown mustard |
| 1 | 310-340 | Soft | Tomato paste |
| 2 | 265-295 | Normal | Peanut butter |
| 3 | 220-250 | Firm | Vegetable shortening |
| 4 | 175-205 | Very firm | Frozen yogurt |
| 5 | 130-160 | Hard | Smooth pate |
| 6 | 85-115 | Very hard | Cheddar cheese |
Typical Applications
| Grade/Class | Common Applications |
|---|---|
| 000, 00 | Centralized lubrication systems, gearboxes requiring semi-fluid grease |
| 0, 1 | Centralized systems, low-temperature applications, high-speed bearings |
| 2 | General-purpose bearing lubrication, most common grade |
| 3 | High-temperature applications, water-exposed equipment, vertical shafts |
| 4, 5, 6 | Block grease for slow-speed plain bearings, specialty applications |
Notes & Limitations
- - NLGI grade indicates only consistency, not quality or performance
- - Grade 2 accounts for approximately 70% of all grease sold
- - Penetration is measured after 60 double strokes of working (worked penetration)
- - Temperature significantly affects grease consistency—a Grade 2 at high temperature may behave like Grade 1
Sources
- NLGI Lubricating Grease Guide
- ASTM D217 - Cone Penetration of Lubricating Grease
- ASTM D4950 - Automotive Service Grease Classification
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