Key Factors for Determining Bearing Tolerance

Key Factors for Determining Bearing Tolerance


Wondering how you can determine the right bearing tolerance for your application? With different bearing tolerance classes, nomenclature and symbols, and series from manufacturers, it can be a daunting task when it comes to understanding accuracies for your application. And, if calculated inaccurately, could turn into a bearing slipping on the shaft and result in machine issues and costly downtime.

That’s why we’ve put together a high-level guide that breaks down the three main elements that contribute to identifying accurate bearing tolerances for your shaft and housing unit, as well as a helpful symbol guide from Bearings Limited’s TRITAN® catalog.  

1. Boundary Dimension Accuracy

One of the key components in determining bearing tolerance starts with identifying the boundary dimension accuracy. The boundary dimension accuracy specifically deals with parts on the shaft and the dimensions on the housing mounting, which include the following:

  •  d – Bore diameter
  •  D – Outer diameter
  • B –  Nominal width of the inner ring
  • C – Nominal width of the outer ring

Dimensional accuracy plays a crucial role in determining shaft and housing fits and can be measured using the dimensional deviation, the single plane mean bore deviation, the outer diameter deviation, and the inner and outer ring width deviations. These are notated as:

  • ∆dmp – Single plane mean bore
  • ∆Dmp – Outer diameter deviation
  • ∆Bs – Inner ring width deviation
  • ∆Cs – Outer ring width deviation

Understanding these elements will help you navigate different dimension series from manufacturers, as well as the maximum and minimum values for fits. It’s important to note that these dimensions are standardized across the industry using bearing tolerance classes from ISO, ABMA, and JIS.  

2. Machining Accuracy   

Machining accuracy refers to the variation in boundary dimensions from one single bearing to another. This measurement revolves around precision and can provide a deeper look at the manufacturing process for a given bearing. This plays an important role in choosing tolerances for certain shafts and housings. Some of the most common measures in determining variation include:

  • Vdp – Bore diameter variation in a single radial plane
  • VDp – Outside diameter variation in a single radial plane
  • Vdmp – Mean bore diameter variation
  • VDmp – Mean outside diameter variation
  • VBs – Inner ring width variation
  • VCs – Outer ring width variation

3. Running Accuracy

The running accuracy refers to parts that are on runout of rotating elements, including the values for radial and axial runout of the inner and outer rings. These are most commonly determined using the following measurements:

  • Kia – Radial runout of assembled bearing inner ring
  • Kea – Radial runout of assembled bearing outer ring
  • Sd – Side face runout with reference to bore of the inner ring

Running accuracy is particularly important to measure, as it directly impacts excess vibration and misalignment issues. With the right running accuracy measurements, you can keep vibration at a minimum and avoid misalignment of the assembly during installation.

Bearing Tolerances Guide

4. Bearing Tolerance Classes

ISO, ABMA, and JIS are internationally standardized bearing tolerance classes that feature allowable error limitations. Each of these classes cover a different area of bearing accuracy. This includes all measures of accuracy that vary in proportion to a given bearing size, as well as precision class. These classifications range from 0-6, with 0 serving as standard accuracy and each following number indicating another level of improved accuracy.

More: How to Identify Bearings

Get Additional Resources from Bearings Limited TRITAN Bearing

While determining bearing tolerances can be a challenge, manufacturers like Bearings Limited provide resources, like their TRITAN® catalog, to help you understand how to select the right bearing and calculate the accurate tolerance for your application. For example, you can see how to determine the key accuracies needed to find the right fit for your application using the TRITAN® bearings and power transmission components catalog on page 23.

At IBT, we firmly believe in partnering with the best brands that will offer you the ultimate peace of mind. As an industry-leading bearings experts, Bearings Limited has been around for over 70 years and has been dedicated to making it easy for you to find the solutions that will meet your unique needs.

Select the Right Bearings for Your Application on ShopIBTTRITAN Bearing

Now that you have a better understanding of the key factors for determining bearing tolerance, you’ll be able to choose the right bearing for your application. On ShopIBT, you can shop a range of bearing solutions directly!

If you’re looking for further advice on what would work best for your shaft and housing units, reach out to us today and our bearings and power transmission specialists will walk you through your options!


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