DIN 51502 - Classification of Lubricating Greases
DIN 51502 is one of the most widely used classification standards for lubricating greases. It is based on a series of letters indicating the type of grease or application, the type of base oil, the NLGI class, the upper operating temperature, the water resistance and the lower operating temperature.
This DIN standard is also used when labelling greases on the container or at the lubrication point itself, using a triangle for mineral oil-based greases and a diamond for synthetic oil-based greases.
The following is an example of the classification of a mineral oil-based bearing grease of NLGI 2, with a higher operating temperature of +120°C, with good water resistance and a lower operating temperature of -30°C. The following tables also show how each letter or number is assigned to the various positions.
Tab. 1 - Prefix letters and symbols for greases
| Type of grease | Letter |
| Greases for rolling and plain bearings and sliding surfaces according to DIN 51 825 (see appendix 1) | K1) |
| Greases for enclosed gear drives, according to DIN 51 826 (see appendix 2) | G |
| Greases for open gear drives (bitumen-free) | OG |
| Greases for plain bearings and seals | M2) |
| Additional letters to indicate the type of synthetic base oil with which the grease has been formulated, if it is a synthetic base oil. | According to tab. 5 |
Symbols
Mineral greases
Synthetic greases
Tab. 2 – NLGI Consistency Grades
| NLGI grade | Worked penetration at 0.1 mm - DIN ISO 2137 | Description |
| 000 | 445 – 475 | Very Fluid |
| 00 | 400 – 430 | Fluid |
| 0 | 355 – 385 | Semi-fluid |
| 1 | 310 – 340 | Very Soft |
| 2 | 265 – 295 | Soft |
| 3 | 220 – 250 | Firm |
| 4 | 175 – 205 | Moderately Hard |
| 5 | 130 – 160 | Hard |
| 6 | 85 - 115 | Very Hard |
Tab.3 – Additional letter for maximum temperature and water resistance
| Letter | Maximum operating temperature | Water resistance (DIN 51807-1 part 1) |
| C | +60ºC | 0-40 or 1-40 |
| D | 2-40 or 3-40 | |
| E | +80ºC | 0-40 or 1-40 |
| F | 2-40 or 3-40 | |
| G | +100ºC | 0-40 or 1-40 |
| H | 2-40 or 3-40 | |
| K | +120ºC | 0-40 or 1-40 |
| M | 2-40 or 3-40 | |
| N | +140ºC |
Subject to agreement |
| P | +160ºC | |
| R | +180ºC | |
| S | +200ºC | |
| T | +220ºC | |
| U | > 240ºC |
Tab.4 - Numbering for lower temperature
Number | Minimum operating temperature |
-10 | -10ºC |
-20 | -20ºC |
-30 | -30ºC |
-40 | -40ºC |
-50 | -50ºC |
-60 | -60ºC |
Tab.5 – Type of synthetic base oil
Identifying Letter | Type of Synthetic Base Oil |
E | Ester |
FK | Perfluorinated polyether |
HC | Synthetic Hydrocarbon |
PH | Phosphoric ester |
PG | Polyglycol |
SI | Silicone Oil |
X | Other |
Appendix 1. DIN 51825 - Requirements for "K" lubricating greases
DIN 51825 specifies the minimum requirements for lubricating greases with the code letter "K" for the lubrication of rolling bearings, plain bearings and sliding surfaces; therefore it only applies to greases of consistencies between 1 and 4. Depending on the additives, the letter K may be followed by another letter, as follows:
| KP | Contains additives to reduce friction and wear or increase load capacity. |
| KF | Contains solid lubricants. |
| KPF | Contains both additives to reduce friction and wear or to increase load-carrying capacity and solid lubricants. |
Appendix 2. DIN 51826 - Requirements for "G" lubricating greases
DIN 51826 specifies the minimum requirements for lubricating greases with the code letter "G" of NLGI classes 000 to 2 for the lubrication of drive elements, particularly enclosed gearboxes.
