NTN Bearing Tolerances

Bearing tolerances, i.e., dimensional accuracy, running accuracy, etc., are regulated by standards such as ISO and JIS. For dimensional accuracy, these standards specify the tolerances and allowable error limits of the boundary dimensions (inner diameter, outer diameter, width, assembled bearing width, chamfer, and taper) required when installing the bearing on the shaft in the bearing housing. For machining accuracy, the standards provide allowable variation limits on bore, mean bore, outside diameter, mean outside diameter, and raceway width or wall thickness (for thrust bearings). Running accuracy is defined as the allowable limits for bearing runout.

Bearing runout tolerances are included in the standards for inner and
Outdoor ring radial and axial runout; inner ringside runout with bore and outer ring outside surface runout with sid Tolerance and allowable error limitations are established for each tolerance grade or class. For example, JIS standard B 1514 (tolerances for rolling bearings) establishes five tolerance classifications (classes 0, 6, 5, 4, 2). Starting from class 0 (average precision class bearings), the bearing precision becomes progressively more significant as the class number becomes smaller. A comparison of relative tolerance class standards between the JIS B1514 standard classes and other standards is shown in the comparative Table 4.1.
Table 4.2 indicates which standard and tolerance class applies to each bearing type.

Size accuracy

Dimensional accuracy is a measure of the outer dimensions of the bearing, such as bore diameter (d), outer diameter (D), inner ring width (B), and outer ring width (C). The difference between the actual bearing size and the nominal value or target value is called dimensional deviation. The most commonly used measurement methods are the average inner diameter and outer diameter deviation of a single plane (Amp and ADmp) and the inner and outer rings (ABs and ACS). Industry-standard tolerances control these values. Dimensional accuracy is essential for determining the fit between the shaft and the bearing housing.

Machining accuracy

When a series of measurements are taken on a single bearing and compared, the machining (or shape) accuracy measures the dimensional change of the above example. The most commonly used measurement methods are single radial plane hole and outer diameter change (Vdp and VDp), average single plane hole and outer diameter change (Vdmp and VDmp), and inner and outer ring width variation (VBs and VCs). Variation refers to the difference between the most significant and most minor measurement values in a sequence. In contrast, average variation refers to the average difference between consecutive measurements.

Machining accuracy reflects the accuracy of the manufacturing process. It is an important consideration when recommending tolerances for shafts and housings.

Running accuracy

Running accuracy (or runout) is a measure of bearing eccentricity (radial runout) and verticality (bore and outer diameter belt side).

Radial runout of inner and outer rings (Kia and Kea) is the most commonly used measure. Operational accuracy is critical to keep excessive vibration and misalignment of the components to a minimum.

ISO/ABMA/JIS tolerance class

For many years, the allowable error limits of the three aspects of bearing accuracy have been internationally standardized as tolerance levels. Each tolerance class specifies a set of limits (which vary in proportion to the bearing size) for all precision measurements. The following table compares the most recognized standards (please note that each column represents a set of equivalent categories). For ISO, JIS, and DiN standards, bearings with standard accuracy are classified as class 0. Then there is level 6. Since then, the reduced number of stages indicates a gradual improvement inaccuracy. The tapered roller bearings of the ABMA or inch series follow a unique but similar tolerance class system.

Table 4.1 Comparison of tolerance classifications of national standard

Standard	Standard	Tolerance Class	Tolerance Class	Tolerance Class	Tolerance Class	Tolerance Class	Bearing Types
Japanese Industrial Standard	JIS B 1514	Class 0 Class 6X	Class 6	Class 5	Class 4	Class 2	All types
International Organization for Standardization	ISO 492	Normal class Class 6X	Class 6	Class 5	Class 4	Class 2	Radial bearings
	ISO 199	Normal class	Class 6	Class 5	Class 4	—	Thrust ball bearings
	ISO 578	Class 4	—	Class 3	Class 0	Class 00	Tapered roller bearings (Inch series)
	ISO 1224	—	—	Class 5A	Class 4A	—	Precision instrument bearings
Deutsches Institut fur Normung	DIN 620	P0	P6	P5	P4	P2	All types
American National Standards Institute (ANSI) Anti-Friction Bearing Manufacturers (AFBMA)	ANSI/AFBMA Std. 201)	ABEC-1 RBEC-1	ABEC-3 RBEC-3	ABEC-5 RBEC-5	ABEC-7	ABEC-9	Radial bearings (Except tapered roller bearings)
	ANSI/AFBMA Std. 19.1	Class K	Class N	Class C	Class B	Class A	Tapered roller bear- ings (Metric series)
	ANSI B 3.19 AFBMA Std. 19	Class 4	Class 2	Class 3	Class 0	Class 00	Tapered roller bearings (Inch series)
	ANSI/AFBMA Std. 12.1		Class 3P	Class 5P Class 5T	Class 7P Class 7T	Class 9P	Precision instrument ball bearings (Metric series)
	ANSI/AFBMA Sts. 12.2	—	Class 3P	Class 5P Class 5T	Class 7P Class 7T	Class 9P	Precision instrument ball bearings (Inch series)

Table 4.2 Bearing types and applicable tolerance

Bearing Type		standard	Applicable tolerance	Applicable tolerance	Applicable tolerance	Applicable tolerance	Applicable tolerance
Deep groove ball bearing		ISO 492	class 0	class 6	class 5	class 4	class 2
Angular contact ball bearings		ISO 492	class 0	class 6	class 5	class 4	class 2
Self-aligning ball bearings		ISO 492	class 0	—	—	—	—
Cylindrical roller bearings		ISO 492	class 0	class 6	class 5	class 4	class 2
Needle roller bearings		ISO 492	class 0	class 6	class 5	class 4	—
Spherical roller bearings		ISO 492	class 0	—	—	—	—
Tapered roller bearings	metric	ISO 492	class 0,6X	class 6	class 5	class 4	—
Tapered roller bearings	inch	AFBMA Std. 19	class 4	class 2	class 3	class 0	class 00
Tapered roller bearings	J series	ANSI/AFBMA Std.19.1	class K	class N	class C	class B	class A
Thrust ball bearings		ISO 199	class 0	class 6	class 5	class 4	—
Thrust roller bearings		NTN standard	class 0	class 6	class 5	class 4	—
Spherical roller thrust bearings		ISO 199	class 0	—	—	—	—
Double direction angular contact thrust ball bearings		NTN standard	—	—	class 5	class 4	—

The following is a list of codes and symbols used in the bearing tolerance standards tables. However, in some cases, the code
or symbol definition has been abbreviated.

Download a catalog list of NTN bearing tolerances.