When should I use C3 instead of CN (Normal) clearance?

C3 clearance (greater than Normal) is used when the bearing operates at elevated temperatures, has a tight interference fit on the shaft, or both. The extra clearance compensates for thermal expansion and fit-induced reduction. C3 is common for electric motors and pumps.

How does temperature affect bearing clearance?

Temperature causes thermal expansion of bearing components. The inner ring typically heats more than the outer ring, reducing radial clearance. For high-temperature applications, select a larger clearance class (C3, C4, or C5) to ensure adequate operating clearance.

How does interference fit affect bearing clearance?

An interference fit on the shaft expands the inner ring raceway, reducing radial clearance. Similarly, an interference fit in the housing compresses the outer ring raceway. The clearance reduction depends on the magnitude of interference, bearing dimensions, and material. This is why bearings with interference fits often require C3 or greater clearance.

Free Engineering Tool

Bearing Internal Clearance Calculator

Look up radial internal clearance for rolling bearings by bore diameter and clearance class per ISO 5753-1. Covers classes C2, CN, C3, C4, and C5.

ISO 5753-1 Radial Ball Bearings C2 – C5

Results

Radial Clearance Range

—

Midpoint Clearance

—

Clearance Class

—

Bore Range Used

—

All Clearance Classes for Selected Bore

Class	Min (μm)	Max (μm)	Midpoint (μm)

What is Internal Clearance?

Bearing internal clearance is the total distance through which one bearing ring can be moved relative to the other in the radial direction. It is defined by ISO 5753-1 for radial rolling bearings.

Clearance is specified as a range (minimum to maximum) for each bore diameter group and clearance class. The actual clearance of a manufactured bearing falls within this range.

Clearance Classes

Class	Description	Typical Use
C2	Less than Normal	Precision spindles, low noise applications
CN	Normal (default)	General-purpose machinery, standard conditions
C3	Greater than Normal	Electric motors, pumps, elevated temperature
C4	Greater than C3	Heavy interference fits, high temperature
C5	Greater than C4	Very high temperature, large interference fits

Effect of Fit and Temperature

The mounted (operating) clearance is always less than the unmounted clearance due to:

Interference fit — shaft fit expands the inner ring, reducing clearance
Temperature — inner ring typically runs hotter than outer ring

Practical Example

Example — Bearing 6210, bore Ø50 mm, class C3

Given: d = 50 mm, Clearance class = C3

From ISO 5753-1 table (bore range 40–50 mm):

C3 clearance: 20 – 43 μm

Midpoint: (20 + 43) / 2 = 31.5 μm

⚠️ Note: This table applies to radial ball bearings (deep groove, angular contact). Roller bearings, tapered roller bearings, and spherical roller bearings have different clearance tables per ISO 5753-1.

Internal clearance is the total distance through which one bearing ring can be moved relative to the other in the radial direction (radial clearance) or axial direction (axial clearance). It is measured before mounting and is critical for proper bearing function, load distribution, and service life.

Too little clearance causes overheating and premature failure. Too much clearance results in noise and uneven load distribution.

C3 clearance (greater than Normal) is recommended when:

The bearing operates at elevated temperatures (inner ring hotter than outer)
There is a tight interference fit on the shaft
Both conditions apply (common in electric motors and pumps)

C3 is the most commonly specified non-standard clearance class for industrial applications.

Temperature causes thermal expansion of bearing components. The inner ring, which is in contact with the shaft and closer to the heat source, typically heats more than the outer ring.

This differential expansion reduces the radial clearance. For high-temperature applications (above ~70°C on the inner ring), select a larger clearance class (C3, C4, or C5) to ensure adequate operating clearance remains.

An interference fit on the shaft expands the inner ring raceway, directly reducing radial clearance. The amount of clearance reduction depends on:

Magnitude of the interference
Bearing bore diameter and cross-section
Material properties (steel expansion coefficient)

Rule of thumb: clearance reduction ≈ 70–90% of the radial interference on the shaft. This is why bearings with interference fits often require C3 or greater clearance.

The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.