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GRW High Precision Ball Bearings

High precision ball bearings in grades up to ABEC 9 with bores from 1 to 30mm and comparable inch dimensions

Bearing Selector

Inch/Metric Bearing
Desired Bore
Desired Outer Diameter

calibration of bore & outside diameter

In order to achieve a uniform fit of the bearing on the shaft and in the housing it is necessary to limit the diameter tolerances of the bearings. As it is very difficult to control very small tolerances in series production, selective grading may be necessary. Only bearings in the quality grades P5 or ABEC5 or better can be graded into groups of 2.5µm (.0001 inch) or 1.25µm (.00005 inch). The diameter of the shaft and housings must also be graded to allow matching.

Due to technical reasons, it is not possible to supply bearings in only one specific tolerance group.

The following symbols are used for the classification of calibrated bearings:

Table 15: Classification of calibrated ball bearings


In groups of 2.5mm or .0001 inch

In groups of 1.25mm or .00005 inch

Bore d and outside diameter D



Bore d only



Outside diameter D only



623 P5 GPR X4B Y
X4B = bore calibrated in groups of 1.25µm. The outside diameter is not calibrated.

Several tolerance groups result due to calibration.

The relevant group is indicated on the packaging of the bearing, according to the following code:

Table 16 - click to image to enlarge


Code 21:
Bore         -2.5/-5µm
O.D.          0/02.5µm

Code BC:
Bore         -1.25/-2.5µm
O.D.         -2.5/-3.75µm

Code A0:
Bore         0/-1.25µm
O.D.         Not calibrated

Code 02:
Bore         Not calibrated
O.D.         -2.5/-5µm

Method of group classification:

Bore diameter: the smallest measured diameter determines the class

Outside diameter: the largest measured diameter determines the class


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