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Selecting the correct clearance is an important part of miniature bearing specification. Even when two bearings have identical dimensions and basic designs, differences in internal clearance can affect their behavior after installation and during operation.
For OEM engineers, equipment manufacturers, and bearing procurement teams, choosing between C0/CN, C2, and C3 requires more than comparing clearance codes. Shaft and housing fits, operating temperature, rotational speed, and applied loads all influence the clearance required by an application.
This guide explains the differences between C0/CN, C2, and C3 miniature bearing clearance, how mounting conditions and temperature affect operating clearance, and what to consider when specifying miniature ball bearings for OEM assemblies or replacement applications.
Radial internal clearance is the total radial distance one bearing ring can move relative to the other, from one extreme position to the opposite extreme position, under specified measuring conditions.
For miniature ball bearings, radial internal clearance is an important specification because compact assemblies often have limited installation space and carefully controlled dimensional requirements.
However, the initial clearance of a new bearing is not necessarily the clearance available after installation. It is important to distinguish between three stages.
Initial radial clearance is the clearance measured in a bearing before it is installed in its shaft and housing. It is generally the value used to identify the bearing's clearance group.
Depending on the bearing series and manufacturer's designation, miniature bearings may be supplied with different clearance options, including C2, normal clearance, and C3.
The specified clearance range depends on the bearing design, bore diameter, and applicable standard or manufacturer specification. A clearance code should therefore be checked against the relevant product documentation rather than interpreted as one universal numerical value.
When a miniature bearing is installed, the fit between its rings and the shaft or housing can change the internal clearance.
For example, an interference fit between the shaft and inner ring can expand the inner ring and reduce radial internal clearance. An interference fit between the housing and outer ring can compress the outer ring, which may also reduce clearance.
The resulting change is influenced by:
Shaft and housing dimensions
Actual interference or clearance fit
Bearing ring geometry and material
Installation method
Assembly conditions
This means that selecting a bearing based only on its initial clearance may not provide the required clearance after installation.
Operating radial clearance is the clearance remaining when the bearing runs under its actual operating conditions.
It can be affected by mounting fits, temperature differences between the inner and outer rings, applied loads, and other operating factors.
A simplified conceptual relationship is:
Operating radial clearance = Initial radial clearance − Mounting-related clearance reduction ± Thermal effects
The thermal effect can either reduce or increase clearance, depending on the relative temperatures and thermal expansion of the inner and outer rings.
This relationship illustrates the main influences on operating clearance; it is not a substitute for an engineering calculation. For applications with tight tolerances or significant temperature changes, the expected operating clearance should be evaluated using the actual bearing dimensions, fits, materials, and operating conditions.
C0/CN, C2, and C3 identify different groups of initial radial internal clearance. The main difference is how each group compares with normal clearance.
| Clearance designation | General meaning | Typical selection consideration |
|---|---|---|
| C2 | Smaller than normal clearance | Applications requiring a smaller initial clearance |
| C0/CN | Normal clearance | Applications designed around the manufacturer's normal clearance range |
| C3 | Greater than normal clearance | Applications where mounting or operating conditions may require greater initial clearance |
The actual clearance range depends on the bearing type, dimensions, applicable standard, and manufacturer specifications.
CN is commonly used to identify the normal clearance group, while C0 is also used as a normal-clearance designation in some bearing catalogues and product systems. Their exact usage and interchangeability should be confirmed against the relevant bearing standard or manufacturer's documentation. They should not automatically be treated as identical markings across all miniature bearing series.
C0 or CN generally refers to the normal radial internal clearance group for a bearing series.
It is often used as a reference when specifying a standard miniature ball bearing. When shaft and housing fits, operating temperatures, and loads are within the manufacturer's recommended conditions, normal clearance can be an appropriate starting point.
However, normal clearance should not automatically be considered suitable for every assembly. A tight shaft fit, housing fit, or temperature difference between the bearing rings may change the clearance after installation.
Before confirming a normal-clearance bearing, engineers should check whether the mounting and operating conditions are consistent with the manufacturer's recommendations.
C2 indicates a radial internal clearance smaller than the normal clearance group.
It may be considered when an application requires a smaller initial clearance and the assembly conditions support that choice.
For example, C2 may be evaluated when the required operating clearance is relatively small and the expected reduction caused by mounting fits and temperature changes will not make the remaining clearance insufficient.
However, selecting C2 does not automatically provide higher bearing precision, lower noise, or longer service life. These characteristics depend on other bearing specifications and operating conditions.
If mounting interference or thermal expansion reduces the clearance excessively, a C2 bearing may develop unsuitable operating conditions, potentially increasing friction and heat generation.
For this reason, C2 should be selected after evaluating the shaft fit, housing fit, and expected operating temperature.
C3 indicates a radial internal clearance greater than the normal clearance group.
It may be considered when the expected clearance reduction during mounting or operation needs to be accommodated. For example, certain assemblies with interference fits or significant thermal effects may require greater initial clearance to achieve the intended operating condition.
However, C3 is not automatically a high-speed bearing specification. A higher clearance code does not independently determine the maximum rotational speed or overall bearing performance.
If the operating clearance is too large for the application, it may affect radial positioning and running stability. Therefore, C3 should be selected based on the complete assembly and operating requirements, not simply because the bearing runs at a high speed.
Mounting fits and thermal expansion are two important factors that determine how much initial radial clearance remains when a miniature bearing is operating.
Understanding these influences helps engineers avoid selecting a clearance group that is unsuitable for the assembled bearing.
Shaft and housing fits directly influence the dimensions of the bearing rings after installation.
When the inner ring is mounted with an interference fit, it can expand and reduce internal clearance. Similarly, an interference fit between the outer ring and housing can compress the outer ring and reduce clearance.
The resulting clearance change is influenced by the interference amount, bearing ring geometry, material properties, and mounting arrangement.
For miniature bearing assemblies, where available space and dimensional tolerances are often limited, even relatively small dimensional changes may be relevant.
When specifying a bearing, engineers should consider:
Shaft diameter and tolerance
Housing bore diameter and tolerance
Required shaft-to-bearing fit
Required housing-to-bearing fit
Expected clearance after installation
Choosing C2, C0/CN, or C3 without considering these factors can result in an unsuitable operating clearance.
Temperature differences between the inner and outer rings can also change radial internal clearance.
If the inner ring becomes hotter than the outer ring, it may expand more and reduce the internal clearance. If the outer ring becomes hotter, its expansion may increase the clearance.
The actual thermal effect depends on the temperature distribution, bearing materials, surrounding components, and operating conditions.
This is particularly relevant to miniature bearings used in compact motors, precision instruments, automation equipment, and other assemblies where heat dissipation may be limited.
For applications with elevated operating temperatures or noticeable temperature differences between bearing rings, clearance selection should account for thermal expansion rather than relying solely on the initial clearance designation.
The operating clearance influences the internal contact conditions between rolling elements and raceways. Its effects can be observed in several aspects of bearing operation.
Friction and heat generation
If operating clearance becomes excessively small, internal contact conditions may become unfavorable, potentially increasing friction and heat generation.
Radial movement and positioning
Excessive clearance can allow more radial movement within the bearing. This may be undesirable in assemblies that require stable shaft positioning or controlled radial movement.
Noise and vibration
Clearance is one factor that can influence bearing noise and vibration, but it is not the only one. Bearing manufacturing quality, surface condition, lubrication, installation, and operating loads also contribute.
Load distribution and contact conditions
Internal clearance affects how loads are distributed between rolling elements and raceways. The actual contact conditions depend on the applied load, bearing geometry, and operating clearance.
The objective is not to select the smallest possible clearance. It is to achieve a suitable clearance under the actual operating conditions.
There is no single clearance code suitable for every miniature bearing application. The correct choice depends on the required operating clearance and the conditions under which the bearing will be installed and used.
The following considerations can help engineers and procurement teams narrow down the appropriate specification.
For applications with conventional mounting arrangements and operating temperatures within the manufacturer's recommended range, normal clearance (C0/CN, where applicable) can be a reasonable starting point.
Before confirming this option, check:
Whether shaft and housing fits are within the recommended range
Whether the expected operating temperature is relatively stable
Whether the applied loads are compatible with the bearing design
Whether the manufacturer's standard clearance range meets the application requirements
Normal clearance is a reference option, not a universal solution. The final selection should be confirmed against the actual assembly conditions.
When a miniature bearing is installed with interference fits, the initial clearance may decrease after mounting. Temperature differences between the inner and outer rings may further change the clearance during operation.
In these situations, C3 may be worth evaluating if the expected clearance reduction means that normal initial clearance would be insufficient.
However, a C3 designation should not be selected automatically. Engineers should assess the actual interference, thermal conditions, and required operating clearance before confirming the specification.
For demanding applications, consulting the bearing manufacturer about the expected post-mounting and operating clearance is recommended.
Some miniature bearing assemblies require carefully controlled radial movement and positioning.
C2 may be considered when a smaller initial clearance is required and the mounting and operating conditions are compatible with it.
Typical application areas may include:
Compact servo motors
Precision instruments
Medical equipment
Small automation systems
Compact drive assemblies
These applications do not automatically require C2 clearance. The correct specification depends on shaft and housing fits, operating temperature, loads, and the performance requirements of the complete assembly.
It is also important to distinguish internal clearance from bearing precision. Clearance and dimensional or rotational accuracy are separate specifications and should be evaluated independently.
Several common assumptions can lead to incorrect clearance selection during miniature bearing sourcing and assembly.
1. Choosing C3 Simply Because the Bearing Runs at High Speed
A high-speed application does not automatically require C3 clearance. Speed is only one part of the operating conditions. Mounting fits, temperature, load, lubrication, and bearing design must also be considered.
2. Ignoring Clearance Reduction After Mounting
Selecting a bearing based only on its initial clearance can lead to an unsuitable result after installation. Always evaluate the effect of actual shaft and housing fits on the bearing rings.
3. Treating Bearing Clearance as a Precision Grade
C2 does not automatically indicate higher dimensional or rotational accuracy. Internal clearance and bearing precision are separate specifications and should be confirmed independently.
4. Applying Clearance Values Without Checking the Bearing Series
Clearance ranges may vary with bearing dimensions, series, and applicable specifications. Do not apply a numerical range from one bearing size or manufacturer to another without verification.
Some manufacturers also use dedicated miniature bearing clearance classifications, such as MC groups. These designations should not be treated as direct equivalents of C2, C0/CN, or C3 unless the manufacturer provides a confirmed comparison.
Whether you are sourcing miniature bearings for a new OEM assembly or replacing an existing bearing, confirming the clearance requirement alongside the bearing dimensions and mounting conditions helps reduce specification mismatches during procurement.
Providing complete application information also helps the supplier review whether the requested clearance is suitable for the intended operating conditions.
When requesting a quotation, prepare the following details where available:
| Required information | Details to provide |
|---|---|
| Bearing part number | Existing model or required bearing designation |
| Required clearance | C2, C0/CN, C3, or a specified clearance range |
| Shaft fit | Shaft diameter and tolerance |
| Housing fit | Housing bore diameter and tolerance |
| Operating temperature | Normal and maximum operating temperatures |
| Rotational speed | Required operating speed in rpm |
| Load conditions | Radial load, axial load, or combined loading |
| Quantity | Sample quantity and estimated production or purchasing volume |
If the existing bearing model is unavailable, also provide the bore diameter, outside diameter, and width.
TOJO's miniature bearing range includes metric and inch series for different equipment and sourcing requirements. You can explore the available product categories:
Need help specifying miniature bearing clearance for an OEM or replacement application?
Contact TOJO with your bearing model, required clearance, shaft and housing fits, operating temperature, rotational speed, and load conditions. Our team can review your requirements and help identify a suitable miniature bearing option.
Request a Quote for Miniature Bearings
C2, C0/CN, and C3 represent different initial radial internal clearance groups, but the correct choice depends on more than the clearance code itself.
Shaft and housing fits, temperature differences, applied loads, and operating conditions all influence the clearance available when a miniature bearing is running.
For OEM engineers, equipment manufacturers, and bearing buyers, the most reliable approach is to evaluate the complete assembly and confirm the required clearance against the manufacturer's specifications. This helps ensure that the selected miniature bearing is suitable for its intended application.
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