The ABEC scale is an industry accepted standard for the tolerances of a ball bearing. It was developed by the Annular Bearing Engineering Committee (ABEC) of the American Bearing Manufacturers Association (ABMA). The ABEC scale is designed to provide bearing manufacturers dimensional specifications that meet the standards of precision bearings in a specified class. Manufacturers who produce equipment that require bearings must also know the dimensional tolerances to design parts that will accommodate a bearing.
There are seven classes from largest to smallest tolerances: 1, 3, 5, 7 and 9. The higher ABEC classes provide better precision, efficiency, and the possibility of greater speed capabilities, but do not necessarily allow the components to spin faster. The ABEC rating does not specify many critical factors, such as load handling capabilities, ball precision, materials, material Rockwell hardness, degree of ball and raceway polishing, noise, vibration, and lubricant. Due to these factors, an ABEC 3 classified bearing could perform better than an ABEC 7 bearing. Bearings not conforming to at least ABEC 1 can not be classified as precision bearings as their tolerances are too loose.
The scale also works as a guide for consumers to make informed decisions about the type of bearing they desire, despite not knowing factors related to materials, manufacturing, and performance.
High rated bearings are intended for precision applications like aircraft instruments or surgical equipment. Lower grades are intended for the vast majority of applications such as vehicles, mechanical hobbies, skates, skateboards, fishing reels and industrial machinery. High ABEC rated bearings allow optimal performance of critical applications requiring very high RPM and smooth operation.
ISO's equivalent standard is ISO 492.
To illustrate the, please see the table. The table shows the actual allowable micron deviations from nominal for a 20 mm inner diameter bearing. As you can see an ABEC 7 bearing only has a 5 micron tolerance window whereas an ABEC 1 has double that at 10 microns. Please see the tables and PDF’s above for more specific precision bearing tolerancing.
There are a number of factors covered by the ABEC grades. One is the eccentricity (roundness) of the track in the inner ring, which determines run-out. The figures given below show the maximum eccentricity allowable.ABEC 1: 0.0075 mm (0.000295")
ABEC 3: 0.0050 mm (0.000197")
ABEC 5: 0.0035 mm (0.000138")
ABEC 7: 0.0025 mm (0.000098")
ABEC 9: 0.0012 mm (0.000047")
ABEC 11: 0.0006 mm (0.0000235")
ABEC 13: 0.0003 mm (0.00001175")