Bearings are essential parts of many types of machinery. They permit the rotating movement by supporting the shaft within a machine like wheels, turbines, gears, and more. There are different types of bearings, such as ball, roller, and thrust bearings, each meant for a specific purpose or requirement.
Choosing the right bearing size is crucial, as improperly sized ones increase friction and premature wear. They also damage the surrounding components, affecting the machinery’s functionality and performance. In this post, we’ll explain bearing size and dimensions in detail.
Basics of Ball Bearing Dimensions
Ball, roller, and plain bearings are the most extensively used bearings across industries. In particular, deep groove ball bearings, angular contact ball bearings, and self-aligning ball bearings are widely employed for high-speed applications with heavy radial loads.
Ball bearing sizes are expressed in millimeters (mm). To measure ball bearing dimensions, you should measure the following:
- Outer diameter (OD)
- Bore size or inner diameter (ID)
- Width or height
Outer diameter (OD)
OD is the measurement across the broadest area of the outer ring of the bearing. This value determines the size of the outer surface where the bearing will fit. To measure it, follow these steps:
- Keep your caliper/micrometer/steel ruler on a flat area.
- Now, place the exterior corners of the measuring instrument’s anvils against the opposite sides of the ball bearing’s outer surface.
- Your tool should be perpendicular to the bearing.
- Note down the reading.
Bore size or inner diameter (ID)
ID is the bearing inner diameter, which is the measurement from one side of the bearing’s inner ring to the other. It is important for the bearing’s contact with the shaft and to determine the size of the shaft. To measure the ball bearing inner diameter, follow these steps:
- Keep your measuring tool on a flat area.
- Insert the anvils of the tool into the bearing’s bore.
- The measuring tool should be perpendicular to the bore.
- Now, record the number shown.
Width or Height
The width tells you how broad the bearing is. It has a direct impact on the bearing’s performance inside the machine and how much load it can take without failure.
- Place the anvils of your measuring tool around the width of the bearing’s outer ring.
- Align the anvils against the opposite sides of the bearing.
- Note down the reading.
Understanding the Bearing Designation System
The basic bearing designation system defines the bearing prefix and suffix or design, and bearing type.
Bearing Design or Prefix and Suffix
Bearing style is indicated by letters that indicate the type or style of bearing, which can differ from manufacturer to manufacturer. The prefix indicates the parts used by the manufacturer to design the bearing. For instance, the (S) indicates the material, which is the stainless steel of the bearing. Common bearing prefixes are mentioned below.
| Prefix | Meaning |
|---|---|
| N | Single row bearing without flanges on the outer ring |
| NU | Single row bearing without flanges on the inner ring |
| NJ | Single-row cylindrical roller bearing with a flange on its inner ring |
| V | Full compliment bearings |
| HJ | Stabilizing ring |
| NUP | Two fixed ribs on the bearing’s outer ring and a fixed rib and a support washer on its inner ring |
| OR | Outer ring of a radial bearing |
| R | Inner or outer ring with a roller and cage assembly of a bearing that can be separated. |
The suffixes indicate the type of seal or shield in the bearing. It differs based on the manufacturer, but the common ones are mentioned below.
| Suffix | Meaning |
|---|---|
| 2RS | Double rubber seals |
| ZZ | Double metal shields |
| UU | Double contact seals |
| CN | Normal clearance |
| N | With snap ring groove |
| K | With tapered bore |
A Note About Bearing Clearance Codes
Bearings with roller elements have additional suffixes. It implies the bearing clearance codes. Bearing clearance is the overall distance a bearing ring can be moved relative to the other one. The two types of bearing clearance are radial clearance, or up-and-down movement, and axial clearance, or side-to-side movement. Improper selection of bearing clearance affects the function and longevity of the bearing. The five clearance classes mentioned for certain bearings are given below.
| Clearance class | Meaning |
|---|---|
| C0 | Normal clearance |
| C2 | Smaller than normal |
| C3 | Greater than normal |
| C4 | Greater than C3 |
| C5 | Greater than C4 |
Bearing Type
Every bearing has a number on its packaging. The first digit of this number tells you the type of bearing. For instance, to find the bearing type from the number 6205, you will look at the first digit, which is 6. It shows that the bearing type is a single-row deep groove ball bearing.
Here’s a look at different type codes and the bearing they indicate:
| Type Code | Bearing Type |
|---|---|
| 1 | Self Aligning Ball Bearing |
| 2 | Spherical Roller Bearing |
| 3 | Double row Angular Contact Ball Bearing |
| 4 | Double Row Ball Bearing |
| 5 | Thrust Ball BearingThrust Ball Bearing |
| 6 | Single Row Deep Groove Ball Bearing |
| 7 | Single Row Angular Contact Bearing |
| 8 | Felt Seal Bearing |
| 32/T | Tapered Roller BearingTapered Roller Bearing |
| R | Inch BearingInch Bearing |
| N | Cylindrical Roller BearingCylindrical Roller Bearing |
| NN | Double Row Roller Bearing |
| NA | Needle Roller BearingNeedle Roller Bearing |
| BK | Needle Roller Bearing with Closed end (Drawn Cup) |
| QJ | Four-point Contact Ball Bearings |
| HK | Needle Roller Bearing with Open ends (Drawn Cup) |
| C | CARB Toroidal Roller Bearings |
| K | Needle Roller and Cage Thrust Assembly |
Next, the second digit tells the bearing series. For example, in the number 6205, the second digit is 2, which tells us that the bearing belongs to the light series.
| Series Code | Series Description |
|---|---|
| 0 | Extra Light |
| 1 | Extra Light Thrust |
| 2 | Light |
| 3 | Medium |
| 4 | Heavy |
| 8 | Extra Thin Section |
| 9 | Very Thin Section |
Lastly, the third and fourth digits show the bore size. To calculate the bore size. multiply the last digit by itself. So, in the number 6205, the bore size will be 5X5, which is 25mm.
Common Ball Bearing Series and Their Sizes
The most common bearing series are:
- 6000 series deep groove ball bearings
- 6200 standard-size deep groove ball bearings
- 6300 deep groove radial ball bearings
- 6700 high-speed ball bearings
- 6800 series deep groove ball bearings
- 6900 series thin high-speed light-duty ball bearings
How to Calculate Bearing Size? Stepwise Approach
To calculate bearing size, you should follow these steps:
- Measure the width, outer diameter, and internal diameter of the bearing.
- Record your measurements in millimeters (mm) because most bearings are measured in metric units.
- Identify the bearing number, which means the prefix, suffix, and bearing type code.
- Lastly, refer to your bearing catalog or manufacturer’s specifications. Use it to find a matching part number based on the dimensions you have recorded.
Consequences of Using Mismatched Bearings
Overlooking the ball bearing size chart leads to the selection of bearings that are unsuitable for your application. As a result, it leads to the following issues:
- Misalignment between the bearing and the shaft results in friction and wear of the bearing components.
- Increased friction causes heat build-up, which degrades bearing material and leads to its failure.
- Uneven load distribution causes the bearing to run inefficiently and disrupts mechanical efficiency.
- The wrong bearings cause noise and prevent the machine from operating smoothly.
When Should You Use a Bearing Size Calculator?
A bearing size calculator allows you to determine load requirements and whether or not a specific bearing size will meet the speed ratings. If your application belongs to the automotive sector, you can use the calculator to predict the bearing’s life expectancy. This is computed based on the load and speed conditions. Calculators also help you to compare bearings according to specific parameters. These include load ratings, dimensions, and lifespan.
Conclusion
Different sizes of bearings are used for various applications according to load ratings and speed requirements. Learning how to calculate bearing size, the number systems followed, and identification is essential to finding the suitable bearing. It also allows you to diagnose and replace damaged ball bearings. You should also stay updated with the latest designs and features of bearings to ensure that your operations are efficient and profitable. Feel free to use our bearing calculator and explore our catalog to find a suitable bearing. As an authorized distributor of ball bearings and industrial products in southern California, we have a fully updated stock of bearings and power transmission tools and provide comprehensive technical support to help you select well-measures bearings for your application.
