How to Read Bearing Numbers: Bearing Codes, Bore Sizes, and Suffixes Explained
Bearing numbers may look like a random combination of digits and letters, but each part usually provides useful information about the bearing type, dimension series, bore diameter, internal clearance, seals, shields, or other design features.
What Does a Bearing Number Mean?
Understanding these codes helps engineers, maintenance teams, and purchasing professionals identify suitable replacement bearings, compare products, and avoid ordering the wrong specification.
Bearing number chart showing how the designation 6205 C3 is divided into bearing type, dimension series, bore diameter, and internal clearance.
The Four Main Parts of a Bearing Number
A common metric bearing designation can be divided into four main sections.
Bearing Type
The first digit, or sometimes the first group of letters, indicates the basic bearing design.
Dimension Series
The second digit usually identifies the bearing dimension series, which relates to its cross-sectional size.
Bore Diameter Code
For many standard metric bearings, the final two digits indicate the internal bore diameter.
Additional Suffix
Letters and numbers after the basic designation can identify internal clearance, seals, shields, cage design, or other features.
1. The First Digit Indicates the Bearing Type
The first digit, or sometimes the first group of letters, identifies the basic bearing design.
In the bearing number 6205, the first digit is 6. In many common metric bearing designations, the number 6 represents a single-row deep groove ball bearing.
Example: Code 6
A bearing number beginning with 6, such as 6204, 6205, or 6306, normally refers to a deep groove ball bearing.
- Low friction
- High rotational speed capability
- Simple construction
- Support for radial loads
- Limited axial load capacity
- Easy installation and maintenance
| Code | Common Bearing Type |
|---|---|
| 0 | Double-row angular contact ball bearing |
| 1 | Self-aligning ball bearing |
| 2 | Spherical roller bearing |
| 3 | Tapered roller bearing |
| 4 | Double-row deep groove ball bearing |
| 5 | Thrust ball bearing |
| 6 | Deep groove ball bearing |
| 7 | Angular contact ball bearing |
| N / NU | Cylindrical roller bearing |
2. The Second Digit Indicates the Dimension Series
The second digit usually identifies the bearing’s dimension series.
The dimension series relates to the bearing’s cross-sectional size, including its outside diameter and width in relation to its bore diameter. In general, a higher series number indicates a larger bearing cross-section and potentially greater load-carrying capacity.
| Code | Dimension Series |
|---|---|
| 0 | Extra-light series |
| 1 | Light series |
| 2 | Medium series |
| 3 | Heavy series |
| 4 | Extra-heavy series |
Comparing 6205 and 6305
6205
A medium-series deep groove ball bearing with a 25 mm bore. It normally has a smaller outside diameter and narrower width than a corresponding 6305 bearing.
6305
A heavy-series deep groove ball bearing with the same 25 mm bore. It normally has a larger outside diameter, greater width, and potentially higher load capacity.
- Available housing space
- Shaft diameter
- Radial and axial loads
- Operating speed
- Required service life
- Installation conditions
3. The Last Two Digits Indicate the Bore Diameter
For many standard metric bearings, the last two digits represent the bore diameter code.
Bore diameter = bore code × 5 mm
For example, code 04 represents a 20 mm bore, code 05 represents a 25 mm bore, and code 06 represents a 30 mm bore.
| Bore Code | Bore Diameter |
|---|---|
| 00 | 10 mm |
| 01 | 12 mm |
| 02 | 15 mm |
| 03 | 17 mm |
| 04 | 20 mm |
| 05 | 25 mm |
| 06 | 30 mm |
| 07 | 35 mm |
| 08 | 40 mm |
Special Bore Codes
Codes 00 to 03 do not follow the multiplication-by-five rule. They represent 10 mm, 12 mm, 15 mm, and 17 mm respectively.
4. Bearing Suffixes Provide Additional Information
Letters and numbers after the basic bearing designation are called suffixes.
Suffixes may indicate internal clearance, seal type, shield type, cage material, precision class, lubrication, heat treatment, snap ring grooves, or a special internal design.
| Suffix | Common Meaning |
|---|---|
| C2 | Internal clearance smaller than normal |
| C3 | Internal clearance greater than normal |
| ZZ | Metal shields on both sides |
| 2RS | Rubber seals on both sides |
| N | Snap ring groove in the outer ring |
| NR | Snap ring groove with snap ring |
Manufacturer Variations
Suffix definitions are not always identical across manufacturers. Before purchasing a replacement bearing, check the relevant manufacturer’s catalogue or technical data sheet.
What Does C3 Mean on a Bearing?
The suffix C3 indicates that the bearing has greater internal clearance than a bearing with normal clearance.
Internal clearance is the total distance through which one bearing ring can move relative to the other before installation.
A C3 bearing may be selected when operating conditions are expected to reduce the internal clearance.
C3 Does Not Automatically Mean Higher Quality
Excessive clearance may increase vibration, noise, or uneven load distribution in applications that do not require it. Clearance should be selected according to fit, temperature, speed, load, and operating environment.
Worked Example: 6205 C3
The complete designation can be divided into four individual pieces of technical information.
Common Bearing Number Examples
The same basic method can be used to understand many common metric bearing designations.
- 6: Deep groove ball bearing
- 2: Medium dimension series
- 04: 20 mm bore diameter
- 6: Deep groove ball bearing
- 3: Heavy dimension series
- 06: 30 mm bore diameter
- 7: Angular contact ball bearing
- 3: Heavy dimension series
- 07: 35 mm bore diameter
- C3: Greater-than-normal clearance
Common Bearing Seals and Shields
The sealing arrangement influences contamination resistance, friction, speed capability, and lubrication retention.
ZZ Metal Shields
A bearing marked ZZ has metal shields on both sides. Metal shields help protect the bearing from larger particles while maintaining relatively low friction.
They are commonly used in electric motors, fans, office equipment, light industrial machinery, and relatively clean environments.
2RS Rubber Seals
A bearing marked 2RS has rubber seals on both sides. Rubber seals generally provide better protection against dust, moisture, and contamination while helping retain grease.
They are commonly used in agricultural machinery, conveyors, outdoor equipment, pumps, and material-handling equipment.
Why Bearing Number Identification Matters
Correctly understanding a bearing designation helps prevent common purchasing, installation, and maintenance problems.
Incorrect Bore Diameter
Similar-looking bearings may have different shaft diameters. Reading the bore code helps confirm whether the bearing fits the shaft.
Incorrect Bearing Series
Bearings with the same bore may have different outside diameters and widths, making them unsuitable for the same housing.
Incorrect Clearance
Selecting the wrong internal clearance may lead to overheating, noise, vibration, or reduced service life.
Incorrect Sealing
Open, shielded, and sealed bearings offer different contamination resistance, friction, and speed capabilities.
Bearing Number Systems Are Not Completely Universal
Bearing numbering systems are useful, but different manufacturers may use different prefixes, suffixes, and internal design identifiers.
Some special bearings also use non-standard product numbers that cannot be decoded using the general rules above.
- Complete bearing designation
- Bore diameter
- Outside diameter and width
- Dynamic and static load ratings
- Speed limit
- Internal clearance
- Seal or shield type
- Cage material
- Precision class
- Operating temperature
- Lubrication specification
- Manufacturer interchange data
Bearing Number FAQ
Quick answers to common questions about bearing codes and suffixes.
What does 6205 mean on a bearing?
6205 generally identifies a single-row deep groove ball bearing from the medium dimension series with a 25 mm bore diameter.
What is the difference between 6205 and 6305?
Both bearings normally have a 25 mm bore. The 6305 belongs to a heavier dimension series and generally has a larger outside diameter, greater width, and higher load capacity.
What does C3 mean after a bearing number?
C3 indicates greater internal clearance than normal. It is often used where tight fits, higher speeds, or elevated operating temperatures reduce bearing clearance during operation.
What is the difference between ZZ and 2RS?
ZZ bearings use metal shields, while 2RS bearings use rubber seals. Metal shields usually create less friction, while rubber seals provide better protection against dust and moisture.
How do I calculate the bore diameter from a bearing number?
For common metric bearing bore codes from 04 upward, multiply the final two digits by 5. For example, code 06 represents a 30 mm bore. Codes 00, 01, 02, and 03 are exceptions.
Are bearing suffixes the same for every manufacturer?
No. Many common suffixes have similar meanings, but manufacturers may use different codes for seals, cages, clearances, lubrication, and special internal designs.
Use Bearing Numbers as a Preliminary Identification Tool
Bearing numbers provide a compact summary of important product information. In a designation such as 6205 C3, the individual characters indicate the bearing type, dimension series, bore diameter, and internal clearance.
Learning how to read these codes can make bearing selection, purchasing, replacement, and maintenance more efficient. However, the numbering system should not be the only selection criterion.
Always compare the complete dimensions, load ratings, speed limits, operating conditions, and manufacturer specifications before confirming a bearing for a particular application.