C3 identifies a radial internal clearance group greater than Normal (CN). It may be needed when mounting fits and operating conditions would otherwise leave too little clearance inside a bearing. C3 is not a precision grade, a temperature rating, or an automatic upgrade over CN.
For a replacement, start with the machine specification and the complete bearing designation. For a new design, select the clearance together with the shaft and housing fits and the expected operating conditions. Do not choose it from the bearing dimensions alone.
What does C3 mean on a bearing?
Radial internal clearance is the total distance one bearing ring can move relative to the other in the radial direction. It is different from the interference between a bearing ring and its shaft or housing seat. A bearing can have C3 internal clearance and still require an interference fit on the shaft.
The clearance group applies to a defined bearing type and size range. The “3” is a designation, not a statement that the gap is three times larger. ISO 5753-1 covers radial internal clearance for several radial bearing types, including deep groove ball, cylindrical roller, and double-row self-aligning roller bearings. The correct table still has to be selected for the actual bearing. See the ISO 5753-1 scope.
Clearance and precision are separate requirements
A C3 suffix does not specify dimensional or running accuracy. If an order requires a particular tolerance class, confirm that separately; do not assume that C3 means P6 or P5. Likewise, C3 does not identify the cage, seals, lubricant, or heat treatment. NSK’s tolerance reference explains the distinction between dimensional and running accuracy requirements.
C3 vs CN vs C4: compare the same bearing type and size
The table below compares the clearance groups conceptually. It is not a dimensional clearance chart.
| Group | Initial radial clearance relative to Normal | Purchasing implication |
|---|---|---|
| C2 | Smaller than Normal | Use only where the required specification supports the reduced clearance. |
| CN / Normal | Normal range | Confirm how the manufacturer identifies the Normal group; it may not appear as a suffix. |
| C3 | Greater than Normal | Confirm that the additional initial clearance is appropriate after mounting and during operation. |
| C4 | Greater than C3 | Do not substitute for C3 simply because the group is larger. |
These relationships are described in NTN’s clearance guide. A clearance group is a range rather than one exact gap. Do not treat an individual bearing as having the midpoint of that range.
Why mounting and operating conditions change clearance
The clearance of an unmounted bearing is not necessarily the clearance available when the machine is running. It helps to separate three stages:
| Stage | What it describes |
|---|---|
| Initial clearance | Clearance before the bearing is mounted. |
| Mounted or residual clearance | Clearance remaining after the rings have been fitted to their seats. |
| Operating clearance | Clearance under the relevant running conditions. |
After fitting
An interference fit can expand the inner ring or compress the outer ring, reducing internal clearance. The result depends on the actual fits and surrounding components, not just the letters on the bearing box.
While running
Temperature differences between the rings can change clearance further. Considering ambient temperature alone misses this effect. Start-up and steady running may also need separate review where their conditions differ.
NSK’s explanation of fits and internal clearance distinguishes the three stages. SKF also identifies fits, initial clearance, and ring temperatures as inputs to operating-clearance evaluation. Neither a hot housing reading nor a tight shaft fit, by itself, establishes the correct clearance group.
When should you consider C3 clearance?
Consider C3 when the equipment specification requires it, or when an engineering review shows that the required operating clearance cannot be achieved with the proposed Normal-clearance bearing and fits. The review should establish the conditions rather than assign a class by industry name.
Useful questions for that review include:
- What shaft and housing fits are specified, and what are their actual measured sizes?
- What temperatures are expected at the inner and outer rings, including during start-up?
- What loads, speeds, and duty cycle must the bearing arrangement support?
- Is the clearance assessed before or after mounting, and by which manufacturer-approved method?
- Has the machine specification changed, or is this a like-for-like replacement?
A motor application does not automatically require C3. Nor does a higher operating temperature automatically justify C4. Clearance selection is also separate from checking the temperature suitability of the lubricant, seals, cage, and other bearing components.
If overheating prompted the inquiry, preserve the operating information before changing the bearing specification. Ordering a larger clearance group without reviewing the arrangement may leave the original problem unresolved.
Can you replace a C3 bearing with a CN bearing?
Do not approve the substitution solely because the basic bearing number and boundary dimensions match. Compare the machine requirement with the full proposed designation, including clearance, seals, cage, and tolerance requirements. Where a change is necessary, obtain the equipment designer’s or responsible engineer’s approval before purchasing.
A replacement example: 6204/C3
Suppose a maintenance parts list calls for 6204/C3, while a supplier’s quotation states only 6204. That quotation is incomplete for approving this particular requirement. Ask the supplier to confirm the clearance group in writing and identify any differences from the requested configuration.
In this example, the ZQM 6204 bearing page identifies the basic product; a required C3 configuration must still be confirmed in the quotation. The same discipline applies when reviewing spherical roller bearings: retain the complete designation rather than dropping a clearance suffix during procurement.
Does C3 tell you the clearance in millimeters?
Not by itself. To obtain an actual range, identify the bearing type, bore-size interval, bore form where relevant, and the manufacturer’s applicable clearance table. Check the units and whether the stated values describe an unmounted bearing or a different condition.
If a datasheet gives only “C3,” request the relevant range when it is needed for engineering approval. Do not use one internet chart for every ball and roller bearing, or transfer values from a different type or size.
What to confirm before requesting a quote
For a straightforward replacement, send the full marking and the equipment parts-list reference. A readable photograph is useful when a suffix is unclear. For a selection review, include the operating information that is available; mark unknown items rather than guessing them.
The following request format keeps the commercial inquiry tied to the technical requirement:
Bearing designation and manufacturer reference:
Required radial clearance group:
Quantity and delivery destination:
Equipment or drawing reference, including revision:
Required seals, cage, and tolerance class, if specified:
Operating speed, load, and ring temperatures, if known:
Changes or substitutions requiring written approval:Browse our deep groove ball bearing range, or send ZQM Bearings your complete designation and quantity to discuss the required configuration and request a quote. Supply details and any proposed alternatives should be confirmed against the order requirements.
Technical references
- NSK: Fits and Internal Clearance.
- NTN Bearing Wizard: Bearing Clearance, Operating Clearance and Preload.
- NSK: Bearing Tolerances.
- ISO 5753-1:2009: public scope and publication information. The clearance tables are not reproduced here.
- SKF Evolution: bearing arrangement evaluation, lubrication, fits, and clearance inputs.