Bearing Precision Classes — ABEC & ISO

What it is

Rolling bearings are made to tolerance classes for bore, outside diameter, width and running accuracy (radial and axial runout). In North America, ABMA 20 uses ABEC classes for radial ball bearings (and RBEC for roller bearings). ISO 492 uses P classes for radial bearings. Higher classes hold tighter tolerances. Precision class is separate from internal clearance (C2, CN, C3 and others), seals and cage type.

How to identify

Standard bearings usually carry no precision mark; they are ABEC 1 or ISO Normal (P0). Higher classes are shown in the suffix, such as P6, P5 or P4, or by an ABEC number on the box. Marking schemes vary by maker. See bearing numbers decoded.

ABEC and ISO classes

Tolerance values for each class are in the ABMA and ISO tables.

Key points

• A higher precision class does not mean a higher load rating. Load ratings come from the bearing size and design.
• Precision helps when runout, noise or speed is critical. In most industrial equipment, a standard class bearing is correct.
• Precision bearings need matching shaft and housing accuracy. A precision bearing on a worn shaft gives standard results.
• Angular contact bearings for spindles are often sold as matched sets with set preload. Replace as a set.
• Handle precision bearings in a clean area and keep them wrapped until use.

Common mistakes

• Ordering ABEC 7 to fix a failure caused by misalignment or contamination.
• Assuming C3 or another clearance code is a precision class.
• Mixing one precision bearing with standard bearings in a matched set.
• Ignoring shaft and housing fits when installing precision bearings.

Governing standards: ABMA 20 (radial bearings of ball, cylindrical roller and spherical roller types, metric design); ISO 492 (radial bearings, tolerances).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.