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Internal Clearance

The internal clearance defines the amount by which one bearing ring can be displaced relative to the other without gauging load.
The internal clearance is not a quality but a design feature.
Taking into account good kinematic conditions, a favourable load distribution inside the bearing and high guiding accuracy, the internal clearance should amount to only a few microns in the installed, ready-to-operate condition.
Radial clearance classes are specified in DIN 620/T4. A distinction is made between:

Radial clearance or radial play; i.e. shifting in radial direction

The amount of the required radial clearance is determined by the fits, the temperatures and the loads.
It must be selected so that the bearing is not deformed (distorted) due to the installation and operation.
The standard radial clearance CN is specified so that sufficient operating bearing clearance remains at customary fits and normal operating conditions.
The lower internal clearance C2 should be provided if bearings are required to be as far as possible without play.
Higher internal clearance C3 or C4 is recommended if special operating conditions prevail such as press fits of the inner ring (e.g. with high speeds) or both bearing rings (e.g. with undefined load direction) or large temperature differences between inner and outer ring.

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Axial clearance or axial play; i.e. shifting in axial direction

The axial clearance is related to the radial clearance.
Depending on the bearing geometry it is 8.5-10 times the radial clearance.
The axial clearance is a design feature, if a defined axial lift is required.

Nominal bore size d mm		Radial clearance in micron
		C2		CN		C3		C4
over	to	min	max	min	max	min	max	min	max
1,5  6 10	6 10 18	0 0 0	7 7 9	2 2 3	13 13 18	8  8 11	23 23 25	- 14 18	- 29 33
18 24 30	24 30 40	0 1 1	10 11 11	5 5 6	20 20 20	13 13 15	28 28 33	20 23 28	36 41 46