Ball Bearing Sizes and Measurement Methods

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General rules regarding verifying ball bearing dimensions and runout are specified in JIS B 1515-2. Please refer to the figures below for the dimensions and measurement methods of runout.

Dimensions

1 Bore (ds) figure 1
2 Outer Diameter (Ds) figure 2
3 Inner Ring Width (Bs) figure 3
4 Outer Ring Width (Cs) figure 4

Runout

1 Side Runout of Inner Ring (Sd) figure 5
2 Outside Cylindrical Surface Runout with Side
   (SD)
figure 6
3 Radial Runout of Inner Ring (Kia) figure 7
4 Radial Runout of Outer Ring (Kea) figure 8
5 Axial Runout of Inner Ring (Sia) figure 9
6 Axial Runout of Outer Ring (Sea) figure 10

Remark: [ ] is the expression in previous JIS.

Bore (ds) Measure the amount of change within the radial plane

Bore (dS) figure 1

Outer Diameter (Ds) Measure the amount of change within the radial plane

Outer Diameter (DS) figure 2

 

Inner Ring Width Measure while rotating inner ring one revolution

Inner Ring Width (BS) figure 3

Outer Ring Width Measure while rotating outer ring one revolution

Outer Ring Width (CS) figure 4

 

Side Runout of Inner Ring Read the indicator while rotating inner ring one revolution

Side Runout of Inner Ring (Sd) figure 5

Outside Cylindrical Surface Runout with Side Read the indicator while rotating outer ring one revolution

Outside Cylindrical Surface Runout with Side (SD) figure 6

 

Radial runout of inner ring Read the indicator while rotating inner ring one revolution with dead weight placed on inner ring

Radial runout of inner ring (Kia) figure 7

Radial runout of outer ring Read the indicator while rotating outer ring one revolution with dead weight placed on outer ring

Radial runout of outer ring (Kea) figure 8

 

Axial runout of inner ring Read the indicator while rotating inner ring one revolution with dead weight placed on inner ring

Axial runout of inner ring (Sia) figure 9

Axial runout of outer ring Read the indicator while rotating outer ring one revolution with dead weight placed on outer ring

Axial runout of outer ring (Sea) figure 10

Ball Bearing Measurement Terms Explained

JIS

JIS B 1515 refers to the Japanese Industrial Standards specifications determined by the Japanese Industrial Standards Committee. The Japanese Industrial Standards (JIS) are published by the Japanese Standards Association and provide a variety of standardized measurements for industrial work, including things such as measurement sizes for a ball bearing. JIS standards are coded with JIS, a letter, and then a number. The letter indicates the specific JIS division. Ball bearing measurements are done according to JIS B 1515 because B is the letter representing the mechanical engineering division. Other divisions include A for civil engineering and architecture, C for electronic and electrical engineering, and D for automotive engineering. Using JIS standards means that you can have more confidence in the quality and functionality of your ball bearings.

Ball Bearing Dimensional Accuracy

The external dimensions of a bearing include the bore diameter (d), the outer diameter (D), the inner ring width (B), and the outer ring width (C). Dimensional accuracy refers to the measurement of error in these dimensions. This measurement is called dimensional deviation: the disparity between the actual bearing dimension and the target value. Dimensional accuracy can be a key value to know when determining housing fits.

Ball Bearing Rotational Accuracy

Another measurement to be aware of when it comes to ball bearings is rotational accuracy, also called running accuracy or “runout.” This is a statistic regarding the degree of eccentricity of a bearing. Bearing measurements of rotational accuracy include side runout of inner and outer ring, radial runout of inner and outer ring, and axial runout of inner and outer ring. The measures most commonly used are radial runout of inner ring (Kia) and radial runout of outer ring (Kea). If a bearing has a high level of radial runout, you can expect that bearing to vibrate more at higher speeds.

Other Bearing Measures Explained

Machining Accuracy

Another measure of bearing accuracy you may encounter is machining, or form accuracy. This is a measure of dimensional accuracy variation across ball bearings, that is, comparing one bearing measurement to another. This measure is an indicator of the level of precision in the manufacturing process.

Bearing Diameter

Another crucial measure of ball bearings is bearing diameter. You will want the measurement for the bore (inside diameter) and the outside diameter. This measurement can be provided in inches or millimeters. The metric system, using millimeters, is most common. Whether you choose a flanged or unflanged bearing will not affect the measurement of the diameter.

Tolerance Classes

There are different international standard measures for bearing tolerance classes. In addition to JIS, which is suitable for all bearing types, there are ISO standards, the standards created by the International Organization for Standardization, and ABMA standards, created by the Anti-Friction Bearing Manufacturers Association. All are suitable for measuring ball bearings depending on the type of bearing you are examining. JIS standards are suitable for all radial ball bearings.

More on Measuring Ball Bearings

It's hard to underestimate the importance of getting the right size ball bearings for your particular applications. In addition to the obvious issue that the wrong size ball bearings simply may not fit, even ones that do fit may not be the most efficient for your application. This could mean your machines run less smoothly, wear out faster, or even break down at a critical juncture. Fortunately, with the precise ball bearings measurements available and the wide range of bearings provided by NMB, it should not be difficult to find the ideal size bearings for your particular needs.

Ball Bearing Size Information

You should easily be able to find the bearings you need using the search options and information on this site. However, if you are having any difficulty at all, do not hesitate to contact NMB with any of your bearing questions. NMB stands behind the quality of every bearing and wants to make sure that you get the bearing you need. Our experts are standing by to discuss bearing measurements, options, and even design issues at any time. If you're in need of quality ball bearings now, don't hesitate to get in touch.