What Is Mỡ NLGI 2? — Bearing Glossary

NLGI 2 grease is a lubricating grease with consistency grade 2 on the National Lubricating Grease Institute (NLGI) classification scale, with penetration measured by ASTM D217 in the range 265–295 × 0.1 mm, and the most widely used consistency grade for rolling element bearings in industry under standard operating temperatures.

The NLGI scale has 9 grades from 000 (fluid, oil-like) to 6 (hard, clay-like). NLGI 1 is softer and flows better but tends to leak at elevated temperatures. NLGI 3 is firmer and stays in place well but restricts lubrication at high speeds and cold temperatures. NLGI 2 is the balance point: firm enough not to be thrown out when the bearing rotates at 3,000 rpm, yet soft enough to flow into the raceway as temperature rises.

Most bearing manufacturer catalogs (SKF, Schaeffler/FAG, NSK, NTN) default to recommending NLGI 2 when no special conditions apply. Factory-lubricated bearings (designated 2RS, 2Z) also use NLGI 2 lithium or lithium complex grease as their standard fill. See the full lubrication guide covering grease selection, intervals, and quantities at bearing lubrication guide and browse deep groove ball bearings pre-filled with NLGI 2 grease.

NLGI 2 Grease Types and Correct Selection

NLGI 2 is only a consistency index — not the sole criterion for grease selection. Three other factors must be considered: thickener type, base oil, and additives.

Common thickeners: lithium (most universal, −20°C to 120°C), lithium complex (improved heat resistance to 150°C), polyurea (high-speed, electrically clean), calcium sulphonate (outstanding water resistance, suitable for wet environments).

Practical example: bearing 6308 C3 (d = 40, D = 90, B = 23 mm, C = 32.5 kN) on an agricultural water pump running at 1,450 rpm, ambient temperature 35–45°C. Standard NLGI 2 lithium grease (such as Shell Alvania 2 or equivalent) is appropriate. Initial fill quantity: 30–50% of free space in the housing. Relubrication interval: every 2,000 hours.