GRW High Precision Ball Bearings
Calibration of bore and outside diameter
High precision ball bearings in grades up to ABEC 9 with bores from 1 to 30mm and comparable inch dimensions
General Information
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
| Calibration | In groups of 2.5mm or .0001 inch | In groups of 1.25mm or .00005 inch |
| Bore d and outside diameter D | X | X4 |
| Bore d only | XB | X4B |
| Outside diameter D only | XD | X4D |
Example:
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:
Examples:Â
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
