ABEC scale
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ABEC (Annular Bearing Engineering Committee) standards define tolerance (engineering) classes for major dimensions and characteristics of steel ball bearings. The ABEC scale of tolerance classes ranges from 1-9 in odd numbers. Higher numbers indicate closer conformance to certain critical bearing dimensions. Bearings manufactured within tighter tolerance ranges provide greater accuracy of shaft rotation and contribute to higher speed capability. However, the ABEC rating does not specify many other critical factors, including raceway uniformity, smoothness of the rolling contact surfaces, ball precision, and material quality.
