Bearing tolerance classes for ball bearing were defined by the American Bearing Manufacturers Association (ABMA) known as the “Annular Bearings Engineers Committee” (ABEC). These tolerances are commonly referred to as ABEC rating or grade. The ABEC tolerance classifications specify both tolerances of size and form for the individual inner and outer rings. The critical features of the rings include the inner ring diameter, outer ring diameter, the ring width and the raceway of each ring.
In China, we use ISO bearing tolerance which start at P0 and then move upwards in precision grade to P6, P5, P4 and P2. ABEC defines 5 classes: ABEC-1, ABEC-3, ABEC-5, ABEC-7, ABEC-9. There are slightly different ABEC tolerance grades for miniature ball bearings and instrument bearings (ABEC-1P, ABEC-3P, ABEC-5P, ABEC-7P and ABEC-9P), and for thin section ball bearings (ABEC-1T, ABEC-3T, ABEC-5T and ABEC-7T).
While the bearing tolerance classes primarily control boundary dimensions of the rings, it should also be noted that there are features that are critical to the bearing performance and life that are not controlled by ABEC(or ISO) specifications. These include: raceway curvatures, internal clearance, surface finish, ball grade level, torque, noise, friction, cage type and lubrication.
Many countries have their own standard organizations, like Germany, Japan etc. In almost all cases, these standards are similar to or state equivalency with ISO 492. The table below shows the equivalent tolerance grades for the most common standards.
| Standard allowable tolerance grades | |||||
|---|---|---|---|---|---|
| GBT307.1 | P0 | P6 | P5 | P4 | P2 |
| ISO 492 | Normal Class | Class6 | Class5 | Class4 | Class2 |
| JIS B 1514 | JIS 0 Grade | JIS 6 Grade | JIS 5 Grade | JIS 4 Grade | JIS 2 Grade |
| AFBMA STD.20 | ABEC-1 | ABEC-3 | ABEC-5 | ABEC-7 | ABEC-9 |
The following links are about the ABEC tolerance for inner rings and outer rings: