Precision is more than runout
ISO 492 specifies dimensional and running accuracy for radial ball and roller bearings. P0 represents normal tolerance, while P6, P5, P4 and P2 progressively tighten relevant characteristics.
ABEC is not a universal translation
ABEC classes commonly correspond approximately to P0, P6, P5 and P4, but the standards do not cover identical attribute sets. A procurement specification must name the governing standard and required inspection values.
Match precision to the functional error budget
Higher precision can be wasted if the shaft, housing, spindle or measurement loop is less accurate. Review the complete tolerance chain and thermal behaviour.