How to find bearing numbers by size?

How to find bearing numbers by size?

by Kevin Sweeney
07 December, 2022
7 min read

For Radial ball, Roller, and plain bearings the critical dimensions are bore size, outer diameter, and width.  The dimensions for bearings are expressed in metric and or imperial denominations.

Specifying a bearing by dimensions is important to have the basic information available.

What are the bore, outer diameter, and width dimensional requirements? If you have the dimensions through measurement on the bearing you can determine the size by looking in a bearing catalog. For example, you measure a standard single-row ball bearing having a 17mm bore (b) x 40 mm outer diameter (D) x width (B) 12 mm wide. Looking at the SKF catalog you will find the part number 6203-RS as the correct bearing. Options are included for the enclosure type shielded, sealed, or open giving you many choices.

Deep groove ball bearings

For many applications, the known parameters might only be the shaft size.

If you are designing a bearing for an application you may only know the shaft dimension and are open to variables in the outer and or width dimensions. Contrarily you may have to keep a fixed size on the width or outer diameter with the ability to change shaft dimensions.

In all of these cases, the next step after identifying acceptable dimensions and identifying the part number is to review the operating life, and conditions of operation including load and speed ratings.

Types of bearings such as a single row, double row, and so on must be determined based on application criteria.  In most applications, ball bearings are subjected to some combination of thrust and radial loads. It is impractical to list bearing capacities for extremely diversified conditions. Therefore catalog load ratings are given for radial loads only and it becomes necessary to convert all other loads to their radial equivalent. The use of combined load factors shown in bearing catalogs engineering sections makes it possible to convert the computed thrust or combined loads in an “equivalent radial load”. The use of the equivalent load allows for the use of the radial capacity tables for all conditions of load that may actually exist.

Other factors which may be directly considered in choosing a bearing are operating speed and desired life or hours of operation. By using Life (L) and speed factors (N) it is possible to select a bearing size to give any average life desired when operating under any constant conditions of load and speed.

Applied calculation examples

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Written by

Kevin Sweeney

Founder and CEO at Pacific International Bearing Sales Inc (PIB)
Education: BS Business and Economics California State University Hayward Ca
CBS (Certified Bearing Specialist)

My role with Pacific International Bearings (PIB) is currently CEO. Since 1976, I have been deeply involved in the bearing industry, working in manufacturing sales at NTN Bearing and subsequently in Bearing Distribution. Before establishing PIB in 1990, I gathered valuable experience in bearing manufacturing and distribution. The last 45 + years in the bearing industry have been both rewarding and challenging, assisting customers across a large number of diverse bearing applications.
Outside of the bearing industry, my interests are family, woodworking, motorcycling, cars, gardening, and golf.
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