NLGI stands for the National Lubricating Grease Institute, a professional organization that created the standard numbering system used to classify grease by its consistency, or stiffness. When you see “NLGI 2” on a tube of grease, that number tells you how thick or thin the grease is on a scale from 000 (nearly liquid) to 6 (a solid block). It’s the single most important number for choosing the right grease for a job.
How the NLGI Scale Works
The NLGI scale has nine grades. Each one corresponds to a specific range of stiffness, measured by a standardized test where a weighted metal cone is dropped into a sample of grease. The deeper the cone sinks, the softer the grease. Penetration depth is measured in tenths of a millimeter at 25°C (77°F).
Here’s the full scale with food-based comparisons that make the differences intuitive:
- 000: Semifluid, close to a thick cooking oil (penetration 445–475)
- 00: Semifluid (penetration 400–430)
- 0: Very soft, like applesauce (penetration 355–385)
- 1: Soft, like tomato paste (penetration 310–340)
- 2: Medium, like peanut butter (penetration 265–295)
- 3: Semihard, like butter (penetration 220–250)
- 4: Hard, like frozen ice cream (penetration 175–205)
- 5: Very hard (penetration 130–160)
- 6: Solid block, like a firm cheese (penetration 85–115)
NLGI 2 is by far the most common grade. It’s the standard for automotive wheel bearings, general-purpose shop grease, and most grease guns. If a product just says “grease” without specifying a grade, it’s almost certainly a 2.
NLGI Grade Is Not the Same as Viscosity
This is where people get tripped up. The NLGI number describes the consistency of the finished grease product: how stiff it feels and how easily it flows. Viscosity, on the other hand, refers to the thickness of the base oil inside the grease. Two greases can share the same NLGI grade but have very different base oil viscosities, which affects how well they lubricate under load and at various speeds.
Think of it this way: consistency is about whether the grease stays put or runs. Viscosity is about how well the oil film actually protects metal surfaces once the grease is in place. You need to match both to the application, not just one.
How to Pick the Right Grade
Three factors drive the decision: temperature, speed, and whether the grease needs to travel through lines or fittings.
In cold environments, a stiffer grease becomes even harder and may not pump through a grease gun, fitting, or centralized lubrication line at all. The colder it gets, the more you need to drop down to a softer grade (lower number) so the grease can actually reach the bearing. Specialized tests measure the lowest temperature at which a grease can practically be pumped, and this threshold varies significantly between grades.
Speed matters too. Faster-moving bearings generate more heat and need the lubricant to flow into the contact zone quickly. A softer, lower-numbered grease feeds into high-speed bearings more readily. Slower, heavily loaded equipment benefits from a stiffer grease (higher number) that won’t squeeze out or fling off under pressure.
A higher-consistency grease stays in place better under heavy loads, but it’s harder to push through grease fittings and lines, especially in the cold. That tradeoff is the core of NLGI grade selection.
Where Each Grade Range Gets Used
Grades 000 through 0 are semifluid to very soft. These behave almost like thick oils and are used in enclosed gearboxes and centralized lubrication systems where the grease needs to flow continuously through long lines, nozzles, and fittings under pressure. You won’t find these in a typical grease gun cartridge.
Grades 1 through 3 cover the vast majority of everyday applications. Grade 1 works well in cold-weather equipment and some automated dispensing systems. Grade 2 handles automotive bearings, chassis components, industrial bearings, and most general maintenance. Grade 3 suits applications where the grease needs to resist being thrown off, like vertical shafts or equipment exposed to vibration.
Grades 4 through 6 are specialty products. They’re hard enough to hold their shape without a container, which makes them useful in slow, heavily loaded applications like open gears or certain dam mechanisms. Most people will never encounter these grades.
What GC-LB Means on the Label
Beyond the NLGI number, you may see a “GC-LB” certification mark on automotive grease. This is a performance standard that NLGI developed with ASTM International in 1989 and that many vehicle manufacturers now write into their specifications.
The two letters after the dash refer to different parts of the vehicle. “G” grades (GA, GB, GC) rate performance in wheel bearings, with GC being the highest. “L” grades (LA, LB) rate performance in chassis components like ball joints and tie rod ends, with LB being the highest. A grease marked GC-LB meets the top standard for both. If you’re shopping for automotive grease and want one product that covers wheel bearings and chassis points, GC-LB is what to look for.
Reading a Grease Label
A typical grease product name might read something like “Lithium Complex EP Grease, NLGI 2, GC-LB.” Here’s what each piece tells you. The first part (lithium complex) identifies the thickener type, which affects temperature range and water resistance. “EP” stands for extreme pressure, meaning the grease contains additives to protect metal under heavy loads. “NLGI 2” is the consistency grade. And “GC-LB” confirms it meets the top automotive performance certification.
For most passenger vehicles, an NLGI 2 grease with GC-LB certification covers wheel bearings and chassis lubrication points. For industrial or specialty equipment, check the manufacturer’s manual for the recommended NLGI grade and base oil viscosity. Those two numbers together, not just one, determine whether the grease will actually protect the component.