Industrial MRO Reference Library · Lubricants & Compatibility
NLGI Grease Grades & Thickeners
What the NLGI consistency number means, how it is measured, and how thickener type and base oil — not the NLGI grade — decide most of a grease's performance and compatibility.
Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.
What it is
A grease is a base oil held in a thickener, plus additives. The NLGI grade describes only how stiff the grease is — its consistency — on a scale from 000 (nearly fluid) to 6 (block-like). It is measured by the worked cone penetration test in ASTM D217: a standard cone drops into worked grease for five seconds, and the depth in tenths of a millimeter sets the grade. Softer greases let the cone sink deeper. NLGI 2 is the most common general-purpose grade.
How to identify
The label or product data sheet should show four things: NLGI grade, thickener type (lithium, lithium complex, calcium sulfonate, polyurea, aluminum complex, clay and others), base oil type and viscosity (mineral or synthetic, with an ISO VG or cSt value at 40 °C), and additives such as EP, moly or solid lubricants. Automotive chassis and wheel bearing greases may also carry an ASTM D4950 category (for example GC-LB). Color is a dye and does not identify a grease.
NLGI grades
| NLGI grade | Worked penetration (0.1 mm, ASTM D217) | Consistency | Typical uses |
|---|---|---|---|
| 000 | 445–475 | Semi-fluid | Enclosed gearboxes, centralized systems |
| 00 | 400–430 | Semi-fluid | Gearboxes, centralized systems |
| 0 | 355–385 | Very soft | Centralized systems, cold service |
| 1 | 310–340 | Soft | Cold service, pumpable applications |
| 2 | 265–295 | Medium | General-purpose bearings and chassis |
| 3 | 220–250 | Medium-firm | Larger bearings, vertical shafts, higher speeds |
| 4 | 175–205 | Firm | Special applications |
| 5 | 130–160 | Very firm | Special applications |
| 6 | 85–115 | Block | Block greases for open bearings |
Key points
- The NLGI grade does not tell you load capacity, temperature range or water resistance. Those come from the thickener, base oil viscosity and additives.
- Base oil viscosity matters most for bearing film strength. Match it to the speed and load — the equipment maker or bearing maker specifies it.
- Thickener compatibility matters when changing products. Some thickener pairs soften or harden when mixed; ASTM D6185 is the test practice. When in doubt, purge the old grease fully.
- Polyurea greases are common in electric motor bearings; lithium complex is a common multipurpose choice; calcium sulfonate is favored for wet and heavy-load service. Always confirm against the equipment maker's lubrication specification.
- Food plants may require H1-registered greases for incidental food contact.
Common mistakes
- Treating "NLGI 2" as a full specification.
- Switching a motor from polyurea to lithium grease without purging.
- Choosing a grease by color.
- Using a stiff grade in a centralized system designed for 0 or 00.
Governing standards: ASTM D217 (cone penetration of lubricating grease — basis of NLGI grades); ASTM D4950 (automotive grease classification); ASTM D6185 (grease compatibility evaluation). Equipment maker's lubrication specification.
Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.