What does C3 mean? Bearing internal clearance
C3 means the internal clearance is greater than normal. The difference between C2, normal, C3 and C4, and when to choose C3.
Last updated: 6 November 2026
There is a very small gap between the rings and the balls of a bearing. It is called internal clearance and is measured in microns (µm, a thousandth of a millimetre). The C at the end of the code gives its class.
| Code | Clearance |
|---|---|
| C2 | Less than normal |
| CN (often not written) | Normal |
| C3 | Greater than normal |
| C4 | Greater than C3 |
| C5 | Greater than C4 |
If the code has no C, the bearing has normal clearance. For a 6205 (25 mm bore), for example, normal clearance is about 5–20 µm and C3 is 13–28 µm. Check the manufacturer's catalogue for exact values.
Why clearance matters
A bearing heats up in use. The inner ring is usually hotter than the outer ring, so it expands more and clearance shrinks. A tight fit on the shaft or in the housing also reduces clearance. Once clearance is used up, the bearing runs preloaded, heats up and fails early.
When to choose C3
- Machines running at high temperature (ovens, dryers, hot environments)
- Applications that heat up and run fast, such as electric motors
- Bearings with a tight fit on both the shaft and in the housing
- Heavy work with vibration
When normal clearance is enough
C3 is not needed at normal temperature with a normal fit. Where quiet running and accurate positioning matter, normal or C2 is preferred; an unnecessary C3 can make a bearing noisier.
When replacing a bearing
If the machine has a C3 bearing, replace it with C3; the machine maker chose it for the temperature and fit. To read the code, see how to read a bearing code, and if you are not sure, ask us.