The original system developed by The Timken Company was based on a family of bearings designed around a common roller. By varying the number of rollers and the angle of the raceways, different bearings can be designed for predominantly radial loads (shallow angle) or axial loads (steep angle).
AB inch PAR T-NUMBERING system
The current inch numbering system was developed by the American Bearing Manufacturers Association (ABMA) to accommodate the growing number of new tapered roller bearing applications and designs. This part numbering system has become the international standard for inch-sized bearings.
The ABMA part numbering system was only applied to new bearing series designed after its introduction. Other numbering systems are also in use, including those based on the original numbering system and proprietary part numbers for specialty bearings.
For example:
HM 5 226 49 —
- HM: series prefix
- 5: angularity
- 226: basic series indication
- 49: component designation
- —: modification suffix
1, serial prefix
The series prefix consists of one or two letters that designate the service class for which the bearing is designed.
| Prefix | Class designation |
|---|---|
| EL | Extra light |
| LL | Lighter than light |
| I | Light |
| LM | Medium light |
| M | average |
| HM | Medium heavy |
| H | heavy |
| AH | Heavier than heavy |
| EH | Extra heavy |
| T | Just push |
2, angularity designator
The first digit after the prefix represents the angle coding determined by the angle included in the outer ring.
| External included – Ring corner | Code |
|---|---|
| 0° to 23° 59' 59.99 inches | 1 |
| 24° to 25° 29' 59.99 inches | two |
| 25°30' to 26°59' 59.99 inches | 3 |
| 27° to 28° 29' 59.99 inches | 4 |
| 28°30' to 30°29' 59.99 inches | 5 |
| 30°30' to 32°29' 59.99 inches | 6 |
| 32°30' to 35°59'59.99 inches | 7 |
| 36° to 44° 59' 59.99 inches | 8 |
| 45° and above; excluding impulse | 9 |
3, basic series indication
The two or three digits following the angularity designator are reserved for the basic series designation. See ABMA Standard 19.2 for more information.
Base series indicate the hole size, not the actual hole size. Bigger number = bigger hole.
4, component designation
The last two numeric digits indicate the component number.
5, modification suffix letters
The suffix may consist of one to three letters in predetermined combinations, indicating changes in external form or internal arrangement.
