Bearing numbers may appear to be random combinations of letters and digits, but every character has a specific meaning. A standard bearing code identifies the bearing type, dimension series, bore size, seals, internal clearance, cage material, and other design features.
Learning how to read bearing part numbers helps engineers, buyers, and maintenance technicians quickly identify replacement bearings, reduce purchasing mistakes, and improve equipment reliability.
A typical bearing designation follows this structure:
Prefix + Basic Bearing Number + Suffix
Example: 6208-2RS/C3
- 6 = Deep groove ball bearing
- 2 = Dimension series
- 08 = 40 mm bore
- 2RS = Double rubber seals
- C3 = Increased internal clearance
1. Bearing Number Structure
Most metric rolling bearings follow the ISO bearing numbering system.
Format : Bearing Type + Dimension Series + Bore Code + Suffix
Example: 6307-2RS
| Code | Meaning |
|---|---|
| 6 | Deep groove ball bearing |
| 3 | Dimension series |
| 07 | 35 mm bore |
| 2RS | Double rubber seals |
Bore Size Rule
| Code | Bore Diameter |
|---|---|
| 00 | 10 mm |
| 01 | 12 mm |
| 02 | 15 mm |
| 03 | 17 mm |
| 04 and above | Multiply by 5 |
Examples
- 6204 → 20 mm
- 6206 → 30 mm
- 6208 → 40 mm
- 6210 → 50 mm
- 22220 → 100 mm
Tip: This calculation applies to standard metric bearings. Inch-size bearings use different designation systems.
2. Common Bearing Type Codes
The first digit or letters identify the bearing type.
| Code | Bearing Type | Example |
|---|---|---|
| 6 | Deep Groove Ball Bearing | 6205 |
| 7 | Angular Contact Ball Bearing | 7206 |
| NU/NJ/N | Cylindrical Roller Bearing | NU2208 |
| 2 | Spherical Roller Bearing | 22210 |
| 3 | Tapered Roller Bearing | 30206 |
| UC | Insert Ball Bearing | UC205 |
| UCF | Square Flange Bearing Unit | UCF208 |
3. Bearing Dimension Series
The dimension series determines the bearing’s outside diameter, width, and load capacity.
Common deep groove ball bearing series:
| Series | Features |
|---|---|
| 60 | Extra light duty |
| 62 | Light duty (most common) |
| 63 | Medium duty, higher load |
| 64 | Heavy duty |
Example: 6208 vs 6308
Both bearings have a 40 mm bore, but:
- 6208 – Smaller outside diameter and width
- 6308 – Larger cross-section and higher load capacity
4. Common Bearing Suffixes
Suffixes describe additional bearing features.
Seals & Shields
| Code | Meaning |
|---|---|
| Open | No seals |
| Z | Single metal shield |
| ZZ / 2Z | Double metal shields |
| RS | Single rubber seal |
| 2RS / 2RS1 | Double rubber seals |
2RS vs 2Z
- 2RS provides excellent protection against water, oil, and fine dust.
- 2Z is mainly designed to keep out dry dust while allowing lower friction and higher speeds.
Choose the seal type according to the operating environment.
Internal Clearance
| Code | Meaning |
|---|---|
| C2 | Reduced clearance |
| CN | Normal clearance |
| C3 | Increased clearance |
| C4 | Extra-large clearance |
| C5 | Maximum clearance |
Typical applications:
| Clearance | Application |
|---|---|
| C2 | Precision equipment |
| CN | General machinery |
| C3 | Electric motors, high speed |
| C4 | Heavy load, high temperature |
Example:6208-C3
Cage Material Codes
| Code | Material |
|---|---|
| M | Machined brass cage |
| J | Pressed steel cage |
| TN / TN9 | Glass-fiber reinforced nylon cage |
Examples：2208M → Brass cage 6205TN9 → Nylon cage
5. Common Bearing Prefixes
Prefixes indicate special materials or designs.
| Prefix | Meaning |
|---|---|
| S | Stainless steel |
| F | Flanged bearing |
| H | High-temperature bearing |
Example: S6905
- S = Stainless steel
- 69 = Thin-section series
- 05 = 25 mm bore
6. How to Read Bearing Numbers
Example 1：6208-2RS/C3
| Part | Meaning |
|---|---|
| 6 | Deep groove ball bearing |
| 2 | Dimension series |
| 08 | 40 mm bore |
| 2RS | Double rubber seals |
| C3 | Increased clearance |
Example 2：22212CA/W33
| Part | Meaning |
|---|---|
| 222 | Spherical roller bearing |
| 12 | 60 mm bore |
| CA | Brass cage |
| W33 | Lubrication groove and oil holes |
7. Why Bearing Numbers Matter
Understanding bearing codes helps you:
- Select the correct replacement bearing
- Avoid installation errors
- Improve equipment reliability
- Extend bearing service life
- Choose the right seals, clearance, and cage material
Frequently Asked Questions
What does C3 mean on a bearing?
C3 indicates increased internal radial clearance. It is commonly used in electric motors and applications involving high speeds or elevated operating temperatures.
What does 2RS mean on a bearing?
2RS means the bearing has rubber contact seals on both sides, providing better protection against dust, water, and contaminants.
What does ZZ mean on a bearing?
ZZ (or 2Z) means the bearing has metal shields on both sides. It offers lower friction than rubber seals but provides less protection against liquids.
- How do I calculate bearing bore size?
For metric bearings:
- 00 = 10 mm
- 01 = 12 mm
- 02 = 15 mm
- 03 = 17 mm
- 04 and above = code × 5
For example: 6208 → 08 × 5 = 40 mm
Conclusion
Understanding bearing numbers and bearing codes is essential for selecting the right bearing, ensuring proper installation, and maximizing equipment performance. By learning how to interpret bearing types, bore sizes, dimension series, seals, internal clearance, and cage materials, you can quickly identify the correct bearing for your application and avoid costly replacement mistakes.
Whether you’re sourcing bearings for industrial machinery, automotive equipment, agricultural machinery, or maintenance projects, using the correct bearing designation helps ensure compatibility and long-term reliability.
At MBY, we supply a wide range of high-quality bearings, including deep groove ball bearings, spherical roller bearings, self-aligning ball bearings, bearing units, and customized bearing solutions. If you need assistance selecting the right bearing or finding an equivalent replacement, our technical team is ready to help.
