Bearing tolerances refer to three aspects of accuracy: external dimensional accuracy, machining accuracy, and running accuracy. Bearing tolerances and permissible values for the boundary dimensions and running accuracy of bearings are specified.
Bearing tolerances are standardized by classifying bearings into the following six classes (accuracy in tolerances becomes higher in the order described): 0, 6X, 6, 5, 4 and 2.
These tolerances follow ISO standards, but some countries use different names for them. Tolerances for each bearing class, and organizations concerning bearings are listed in table below.
| Standard | Tolerance Class | Bearing types | |||||
|---|---|---|---|---|---|---|---|
| International organization for standardization | ISO 492 | Normal class class 6X | Class 6 | Class 5 | Class 4 | Class 2 | Radial bearings |
| ISO 199 | Normal class | Class 6 | Class 5 | Class 4 | Class 2 | Thrust ball bearings | |
| ISO 578 | Class 4 | - | Class 3 | Class 0 | Class 00 | Tapered roller bearings (inch series) | |
| ISO 1224 | - | - | Class 5A | Class 4A | - | Precision instrument bearings | |
| German institute for standardization | DIN 620 | P0 | P6 | P5 | P4 | P2 | All types |
| Japanese industrial standard | JIS B 1514 | Class 0 Class 6X | Class 6 | Class 5 | Class 4 | Class 2 | All types |
| American national standards institute (ANSI) | ANSI/AFBMA Std. 20 | ABEC-1 RBEC-1 | ABEC-3 RBEC-3 | ABEC-5 RBEC-5 | ABEC-7 | ABEC-9 | Radial bearings (except tapered roller bearings) |
| ANSI/AFBMA Std. 19.1 | Class K | Class N | Class C | Class B | Class A | Tapered roller bearings (metric series) | |
| ANSI B 3.19 AFBMA Std. 19 | Class 4 | Class 2 | Class 3 | Class 0 | Class 00 | Tapered roller bearings (inch series) | |
| Anti-Friction bearing manufactures (AFBMA) | ANSI/AFBMA Std. 12.1 | - | Class 3P | Class 5P Class 5T | Class 7P Class 7T | Class 9P | Precision instrument ball bearings (metric series) |
| ANSI/AFBMA Std. 12.2 | - | Class 3P | Class 5P Class 5T | Class 7P Class 7T | Class 9P | Precision instrument ball bearings (inch series) | |
1) “ABEC” is applied for ball bearings and “RBEC” for roller bearings.
2) JIS B 1514, ISO 492 and 199, and DIN 620 have the same specification level
3) The tolerance and allowance of JIS B 1514 are a little different from those of AFBMA standards
| Bearing Type | Applicable standard | Applicable tolerance | |||||
|---|---|---|---|---|---|---|---|
| Deep groove ball bearing | ISO 492 | Class 0 | Class 6 | Class 5 | Class 4 | Class 2 | |
| Angular contact ball bearings | Class 0 | Class 6 | Class 5 | Class 4 | Class 2 | ||
| Self-aligning ball bearings | Class 0 | - | - | - | - | ||
| Cylindrical roller bearings | Class 0 | Class 6 | Class 5 | Class 4 | Class 2 | ||
| Needle roller bearings | Class 0 | Class 6 | Class 5 | Class 4 | - | ||
| Spherical roller bearings | Class 0 | - | - | - | - | ||
| Tapered roller bearings | metric | ISO 492 | Class 0,6X | Class 6 | Class 5 | Class 4 | - |
| inch | AFBMA Std. 19 | Class 4 | Class 2 | Class 3 | Class 0 | Class 00 | |
| J series | ANSI/AFBMA Std.19.1 | Class K | Class N | Class C | Class B | Class A | |
| Thrust ball bearings | ISO 199 | Class 0 | Class 6 | Class 5 | Class 4 | - | |
| Spherical roller thrust bearings | ISO 199 | Class 0 | - | - | - | - | |
Dimensional accuracy
Dimensional accuracy is a measure of the bearing's external dimensions, for example bore diameter (d), outer diameter (D), inner ring width (B), and outer ring width (C). The difference between an actual bearing dimension and the nominal or target value is called the dimensional deviation. The most commonly used measures are the single plane mean bore and outer diameter deviations (Admp and ADmp), and the inner and outer ring width deviations (ABs and ACs). These values are governed by industry standard tolerances. Dimensional accuracy is important for determining shaft and housing fits.
Machining accuracy
Machining (or form) accuracy measures the variation in the above example dimensions when a series of measurements is taken on a single bearing and compared to one other. The most common measures are single radial plane bore and outside diameter variation (Vdp and VDp), mean single plane bore and outside diameter variation (Vdmp and VDmp), and inner and outer ring width variation (VBs and VCs). Variation refers to the difference between the largest and smallest measurements in a series, while mean variation refers to the average difference between consecutive measurements.
Machining accuracy reflects the precision of the manufacturing process and is an important consideration when recommending tolerances for shafts and housings.
Running accuracy
Running accuracy (or runout) is a measure of the degree of eccentricity (for radial runout) and squareness (for bore and O.D. with side face) of the bearing.
Inner and outer ring radial runout (Kia and Kea) are the measures most often used. Running accuracy is important to keep excess vibration and misalignment of the assembly at a minimum.
Bearing Tolerance tables
Actual tolerance values are listed in the following tables. The tolerance symbols used in the bearing tolerance standards tables refer to bearing tolerance table.
- Metric radial bearings, except tapered roller bearings
- Metric tapered roller bearings:
- Inch radial bearings, except tapered roller bearings:
- Inch tapered roller bearings:
- Thrust bearings:
- Tapered bore, taper 1:12:
- Tapered bore, taper 1:30:
Tolerance symbols
The bearing tolerance symbols are a list of codes and bymbols which used in the bearing tolerance tables, refer to Bearing tolerance symbols.