Bearing tolerance standards create consistency in manufacturing to ensure a uniform product.
Most manufacturers publish their bearing tolerance standards and make that information readily available for customers. Even though the tolerances are very similar, some slight variations do exist between standards.
Common Bearing Tolerance Standards
In the United States the American National Standards Institute (ANSI) oversees standards and conformity systems. The Annular Bearings Engineers Committee (ABEC) and International Standards Organization (ISO) classes are two subsets of ANSI and the most commonly used to measure precision in bearings.
For European standards you’ll commonly find Deutsches Institut für Normung (DIN) represented.
The table below shows how each standard matches up to it’s equivalent.
|ANSI Standard*||DIN 620*||ISO 492*|
|ABEC 1||P0||Class Normal|
|ABEC 3||P6||Class 6|
|ABEC 5||P5||Class 5|
|ABEC 7||P4||Class 4|
|ABEC 9||P2||Class 2|
*Chamfer and other dimensions may be supported by other standards
Please note: Some bearing manufacturers have created their own tolerance standards (similar to DIN P3), in this article we’re only focusing on nationally recognized standards.
Engineering Design Support
In engineering, the tolerance of the bearing is only half the equation. We have multiple calculators that support engineers in designing the right precision component for different applications.
Our Standards and RPM calculator uses ABEC tolerancing standards to map the dimensions of a users shaft and housing. It then calculates the suggested RPMs needed.
Bearing Tolerance Leadership
The United States uses bearing standard tolerances approved by the American National Standards Institute (ANSI). The standards are presented to them from the American Bearing Manufacturers Association (ABMA).
The standards are actually created and overseen by ABEC, a group under ABMA. ABEC and ABMA carry the weight of the industry and are the primary care takers of bearing tolerancing.
In the 21st Century, all of these standards organizations, including DIN and ISO, work together for a common goal. This goal is achieved by users being able to trust in standards to successfully use precision bearings across many industries around the world.
Precision bearing tolerance classes include tolerance for form, fit, function, and correlated running characteristics of bearings.
This includes but is not limited to:
- Inner Diameter
- Outer Diameter
- Radial Runout
- Face Runout
- Axial Runout
- Profile of a Surface
- And more..
For the ABEC precision classes, the higher the number the tighter the tolerance. In order from loose to tight tolerance you have: ABEC 1, ABEC 3, ABEC 5, ABEC 7, and ABEC 9.
Note that the DIN class is opposite of ABEC from a numerical standpoint. Listed from low precision to high precision: P0, P6, P5, P4, P3, and P2.
Tips on Precision Bearing Pricing
A good hint for engineers and purchasers is that there are larger gaps in pricing and precision between ABEC 3 and ABEC 5, as well as ABEC 5 and ABEC 7.
This means the price and precision difference between ABEC 1 and ABEC 3 is less than ABEC 3 and ABEC 5. When precision machining of bearings was in its infancy, only ABEC 1 bearings were consistently produced. As machining prowess and technology increased, so did the consistency in super precision bearing machining and manufacturing. In the 21st century, ABEC 7 and ABEC 9 bearings are produced consistently and relatively easily.
Practical Advice for Determining Bearing Reliability
An interesting discussion about bearing precision classes vs. running capabilities is probably opposite of what you’d think. Every bearing actually has the same maximum RPM potential.
For example, an S6005 CTA ABEC 7 UL bearing in precision ABEC 7, ABEC 5, or even ABEC 3 would all have the potential to achieve the maximum RPM rating. The difference is which bearing has the actual ability to actually achieve the maximum RPM on a consistent basis.
Here’s an analogy that will help. It’s the 1-10 analogy:
If 10 pieces of an S6005 CTA ABEC 3 UL bearing were purchased, one could expect 3 of the 10 to achieve maximum capabilities. But, if you purchased 10 pieces of the same bearing but ABEC 5, you could expect 5 of the 10 to achieve maximum capabilities. So on and so forth.
This is only a theoretical tip that could help engineers and purchasers understand the difference between precision tolerance classes.
The higher the need for reliability, runout, RPM, etc. the more the cost is justified for a higher precision bearing.
As one’s application reaches higher and higher RPM’s, every micron of parallelism, runout, surface profile, etc. all make a difference.
To consistently run an application at high speeds, a super precision bearing in class ABEC 7 or higher would most certainly be suggested if not required.
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