CN is the normal radial internal clearance group, and the one you receive when the designation carries no clearance suffix at all. Some drawings and catalogues write C0 instead; there is no ISO symbol C0, and the two mean the same thing. CN suits general engineering: rotating inner ring load, a normal interference fit, moderate speed and a temperature rise under about 60 °C.
CN is the group for which the standard interference fits were designed. A k5 or j5 shaft in a CN bearing leaves a small positive clearance at operating temperature, which is the state the bearing was optimised for: enough clearance to avoid preload, little enough to keep the elements loaded and quiet. Deviate only when one of those two assumptions fails.
First, the fit. If the shaft is k6 or m6 instead of k5, the inner ring expands more and the clearance closes. Second, the heat. If the shaft runs 50 °C hotter than the housing — common in fans, hot pumps and dryer rollers — the inner ring grows more than the outer and again the clearance closes. Either condition is a reason to move up to C3, and both are cheap to check before ordering.
| Meaning | Normal radial internal clearance |
|---|---|
| Also written | C0 (not an ISO symbol, but the same group) |
| Default | Yes — applied when the designation has no clearance suffix |
| Assumed fit | Normal interference on a rotating inner ring |
| Assumed temperature rise | Up to about 60 °C above ambient |
| Typical use | General machinery, gearboxes, hand tools, conveyors |
| Availability | Universal |
| Symptom | Likely cause | Move to |
|---|---|---|
| Bearing runs hot at moderate load | Clearance closed by fit or heat | C3 |
| Whining tone that follows speed | Preload from thermal growth | C3 |
| Grease turns dark and hard early | Overheating from preload | C3 |
| Axial play felt in a precision axis | Clearance too large for the duty | C2 |
| Vibration at light load | Elements skidding in a loose bearing | C2 |
Yes. C0 is a widely used shorthand for the normal group; ISO 5753-1 calls it CN. Ordering either gets you normal clearance.
The inner ring expands and consumes the clearance, so the bearing runs preloaded: temperature rises, grease life falls and the raceway can show distress. Use C3 in that case.
Only if you want to be explicit. Leaving the clearance suffix off means CN anyway; writing it prevents a substitution to C3 by a supplier.
Send the designation, the three dimensions and the quantity — we reply with price, brand options and lead time within 30 minutes on working days.