Bearing Clearance: C2, CN, C3, and C4 Explained

Bearing clearance is an important specification that directly affects bearing temperature, vibration, load distribution, and service life.

When selecting a bearing, you may see designations such as C2, CN, C3, or C4. These codes indicate different internal clearance levels.

Choosing the correct clearance is especially important for electric motors, pumps, fans, conveyors, and other rotating equipment.

What Is Bearing Clearance?

Bearing clearance is the internal space between the rolling elements and raceways before the bearing is installed.

After installation, the actual operating clearance can change because of:

• Shaft and housing fits

• Operating temperature

• Thermal expansion

• Load conditions

Therefore, the clearance of an unmounted bearing is not necessarily the same as its clearance during operation.

What Do C2, CN, C3, and C4 Mean?

The common clearance classes can be understood simply:

The exact clearance values depend on the bearing type and bore size, so a C3 bearing does not have one universal clearance value.

When Is C3 Clearance Used?

C3 is one of the most commonly specified increased-clearance options.

It may be appropriate when installation and operating conditions significantly reduce the bearing's effective clearance.

Typical situations include:

• Higher operating temperatures

• Tight shaft fits

• Thermal expansion

• Certain electric motor applications

• Heavy-duty operating conditions

However, C3 is not automatically better than CN.

If an application does not require additional clearance, using C3 may increase internal movement and potentially affect noise, vibration, or running accuracy.

C2 vs CN vs C3 vs C4

A simple rule is:

C2 → tighter

CN → normal

C3 → greater

C4 → even greater

The correct choice should be based on the actual operating conditions rather than simply selecting the largest clearance.

Why Bearing Clearance Matters

Incorrect clearance can cause problems.

Too Little Clearance

Insufficient operating clearance can increase:

• Friction

• Operating temperature

• Contact stress

• Risk of premature failure

Too Much Clearance

Excessive clearance can lead to:

• Increased vibration

• Noise

• Uneven load distribution

• Reduced running accuracy

The objective is to achieve suitable operating clearance, not simply the largest or smallest possible clearance.

How to Choose the Correct Clearance

Before ordering a bearing, consider:

1. Operating temperature

Higher temperature differences may require additional clearance.

2. Shaft fit

A tight interference fit can reduce internal clearance after installation.

3. Housing fit

The housing fit also affects the final operating clearance.

4. Speed and load

Speed, load, lubrication, and heat generation should be considered together.

5. Manufacturer specification

Always confirm the recommended clearance with the bearing manufacturer or supplier.

Don't Confuse C3 With Bearing Precision

One common mistake is assuming that C3 means higher precision or better quality.

It does not.

C3 describes internal clearance, while bearing precision is specified separately through tolerance or precision classes.

Therefore:

C3 ≠ higher precision

C3 ≠ higher quality

It simply means the bearing has greater internal clearance than the normal clearance class.

Why Choose DBS Bearing?

DBS Bearing supplies deep groove ball bearings, tapered roller bearings, pillow block bearings, wheel hub bearings, and other industrial bearing solutions.

We can supply bearings with different clearance and sealing configurations according to application requirements.

If you are unsure whether your application requires CN, C3, or C4 clearance, send us the bearing number, shaft size, operating temperature, speed, and application details.

Our team can help you identify a suitable bearing specification.