ISO class 2 ABMA ABEC9 Precision Bearings

In the United States, the American Bearing Manufacturers Association (ABMA) maintains the standards deemed necessary by its bearing industry member companies. This includes revising existing, or proposing and preparing new standards. These standards are then proposed to the American National Standards Institute (ANSI) for approval as US national standards. ANSI has a committee consisting of representatives from user organizations, manufacturers, and the US government that are devoted to rolling bearing standards activities.

Tolerance classes for ball bearings were defined by a committee within the ABMA known as the “Annular Bearings Engineers Committee” (ABEC). These tolerances are commonly referred to as ABEC rating, or grade. Tolerance classes for roller bearings are covered by the RBEC classifications contained within the same standard. These classes are defined in ABMA standard 20 – Radial Bearings of Ball, Cylindrical Roller, and Spherical Roller Types and ABMA standards 12.1 and 12.2 – Instrument Ball Bearings. The ABEC (and RBEC) tolerance classifications specify both tolerances of size and form for the individual inner and outer rings. The critical features of the rings include the bore (or inner diameter of the inner ring), the outer diameter of the outer ring, the ring widths, and the raceways of each ring. Tolerances of form include roundness, taper, runout, and parallelism.

ABMA standard 20 defines 5 classes: ABEC 1, ABEC 3, ABEC 5, ABEC 7, and ABEC 9. Instrument series ball bearings are defined in standards 12.1 and 12.2 and carry the suffix “P”. Extra thin and thin section ball bearings defined in standards 12.1 and 12.2 carry the suffix “T”. The higher the number of the classification, the tighter the tolerances become resulting in higher precision of the assembled bearing. When the classification system was first set up, machine tool technology was such that manufacturers mass produced only ABEC 1, and sometimes ABEC 3. Bearings for the higher classifications were selected from the production runs of the lower classification. Today, the technology has advanced to the point where manufacturers can produce ABEC 7 and ABEC 9 bearings routinely.