C3 gives the bearing more internal clearance than normal, so that after the interference fit and the thermal expansion there is still running clearance left. It is the standard choice for electric motors, fans, pumps and any position where the inner ring runs hotter than the housing, and it is the single most common special suffix in bearing purchasing.
A motor shaft is a press fit into the inner ring and reaches 70–90 °C in normal running, while the housing stays near ambient. Both effects expand the inner ring relative to the outer, which consumes clearance. If the motor started with CN, it would end up running at zero clearance — measurably hotter, noisier and with a fraction of the expected grease life. C3 gives back that margin.
Fitting C3 where the fit is light and the temperature rise is small leaves more clearance than the bearing wants: the elements skid instead of rolling, vibration at light load rises and the cage takes load it was not designed for. C3 is a correction for a known consumption of clearance, not a default that is always safe.
Many customers ask whether C3 is noisier. In a proper motor application the difference is not audible. Where a noise complaint does appear after switching to C3, the cause is usually a light fit that should have stayed CN, or an axial preload spring that is too stiff.
| Meaning | Radial internal clearance greater than normal |
|---|---|
| Position | One group looser than CN |
| Assumed fit | Medium interference, rotating inner ring |
| Assumed temperature difference | 40–80 °C between inner and outer ring |
| Typical use | Electric motors, fans, pumps, conveyors, gearboxes |
| Effect on life | Neutral to positive where preload would otherwise occur |
| Effect on noise | Marginal increase at low speed and light load |
| Availability | Universal — stocked alongside CN |
| Price | Usually identical to CN |
| Criterion | CN | C3 | C4 |
|---|---|---|---|
| Relative clearance | Normal | Loose | Looser |
| Temperature difference assumed | Under 40 °C | 40–80 °C | 80–120 °C |
| Fit | Normal | Medium interference | Heavy interference |
| Typical application | General machinery | Motors, fans, pumps | Kilns, dryer rollers, large rollers |
| Noise | Reference | +0 to +2 dB | +1 to +4 dB |
| Availability | Universal | Universal | Common in large sizes |
| Cost | Reference | Same | Same to +10% |
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Read →Not in general. C3 is better where clearance would otherwise be consumed by fit and heat. In a light-fit, low-temperature position CN is better because the elements stay properly loaded.
Only marginally, and usually not audibly in a motor. If a C3 bearing is noticeably noisy, check the fit, the alignment and the axial preload before blaming the clearance.
Yes, and it is common where the gearbox runs hot or the shaft fit is heavy. In a cool, lightly fitted gearbox CN is fine.
In most metric sizes, no. C3 is a catalogue variant produced in volume alongside CN, so the price is the same.
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