CN, C3 or C4 — what the clearance suffix means

Short answer

CN is normal clearance — the default the manufacturer assumes for an ordinary fit at room temperature. If nothing follows the last dash in the designation, you have CN.

C3 is increased clearance. You take it wherever something will consume that clearance: a tighter fit on the shaft, an inner ring hotter than the outer one, elevated operating temperature. Typically electric motors, fans, gearboxes.

C4 goes further still — for when two causes meet, say a hot bearing in its housing combined with a tight shaft fit.

Catalogue clearance is clearance BEFORE mounting. Pressing onto the shaft and heating up leave far less of it.

Why the clearance disappears once mounted

An inner ring pushed on with interference expands — the raceway grows and takes part of the clearance with it. That happens before the machine even starts.

The rest goes in service: the inner ring sits on a shaft that heats faster and hotter than the housing, so it expands more than the outer ring. The temperature difference between the rings eats clearance directly.

That is why a C3 bearing feels “looser than it should” when cold and runs exactly as intended under load. Judging clearance by hand on a bearing lying on the bench tells you nothing about the machine.

What the catalogue holds

Across the 11 088 cards that state a clearance group, the split looks like this. C3 is no exception — it is every second bearing.

The harder a type's typical duty, the further its clearance is shifted up — nearly one spherical roller bearing in four is C4.

When C3 is not a choice but the only version

In our catalogue 2 899 designations exist in both CN and C3 — there the choice really is the buyer's. But 1 274 designations exist in C3 ONLY: the manufacturer does not build them with normal clearance, because the application is known in advance.

It shows most clearly on bearings filled with a special grease at the factory (code L0xx in the designation): 445 of them carry C3 against just 209 with normal clearance. These are the high-temperature, long-life-without-relubrication designs — and increased clearance comes as standard.

If a shop lists the C3 version only, that is usually not a stock gap but the absence of any other version at the manufacturer.

Where to read it in the designation

The clearance group sits at the very end, after the last dash: 6205-C3, 6311-C-N-C3, 22332-BE-XL-H151-C3. No suffix means CN — normal clearance is never written out.

Do not confuse it with the accuracy class (P6, P5, P4). Accuracy describes the manufacturing tolerances of the rings; clearance describes the gap between raceway and rolling element. Two independent properties of the same bearing.

What not to do

Never swap C3 for CN because “that was all the shop had”. If the machine ran on increased clearance, the fit and the temperatures have not changed — a normal-clearance bearing will end up with no clearance at all in service and seize.

The other direction deserves care too: more clearance than a cold-running machine needs means noise, run-out and faster raceway fatigue. C4 “to be safe” is not the safe option.

If you do not know what was there before, read the designation off the old bearing — the suffix is stamped on the ring. If it is illegible, write to us with the machine model; our cards carry the clearance group wherever the manufacturer states it.

Dimensions you can measure with a caliper. Clearance you can only read off the designation.