Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D217-21 – Standard Test Method Technical Guide
📐 Scope and NLGI Consistency Classification
The ASTM D217-21a test methods outline four standard procedures for measuring the consistency of lubricating greases using the cone penetration method. The penetration depth, measured in tenths of a millimetre (0.1 mm), determines the consistency grade which correlates directly with the National Lubricating Grease Institute (NLGI) classification system. The methods are applicable to greases with penetrations between 85 and 475, spanning the full range from NLGI 6 to NLGI 000.
| 🟦 NLGI Consistency Number | 📏 Worked Penetration Range (25 °C / 77 °F) |
|---|---|
| 000 | 445 to 475 |
| 00 | 400 to 430 |
| 0 | 355 to 385 |
| 1 | 310 to 340 |
| 2 | 265 to 295 |
| 3 | 220 to 250 |
| 4 | 175 to 205 |
| 5 | 130 to 160 |
| 6 | 85 to 115 |
✔ Note on Worked Penetration: Worked penetrations are generally preferred over unworked values for inspection purposes, as they provide a more reliable representation of the grease consistency under dynamic service conditions.
⚙️ Test Procedures and Applicability
The standard establishes four distinct procedures tailored to different grease types and conditions. The standard procedures for Unworked Penetration, Worked Penetration, and Prolonged Worked Penetration are designed for greases with consistency numbers from NLGI 6 to NLGI 000 (penetrations of 85 to 475). A complementary Block Penetration procedure is provided for greases that are firm enough to hold their shape, typically exhibiting penetrations below 85 tenths of a millimetre. An additional method for Undisturbed Penetration is detailed in Appendix X1.
⚠ Exclusions: None of the procedures in this standard are suitable for measuring the consistency of petrolatums. Users should refer to Test Method D937 for such products. This standard also utilizes SI units as primary units with imperial equivalents provided for reference.
📊 Key Measured Properties and Equipment Specifications
The fundamental measurement in all procedures is the depth, in tenths of a millimetre, that a standard cone of a specified mass and dimensions penetrates the grease sample. All measurements are conducted at a standardized temperature of 25 °C (77 °F). The table below summarizes the applicability of each test procedure.