Boundary dimensions are the main dimensions of a bearing (fig. 1 and fig. 2). They comprise

fig. 1 - Boundary dimensions, radial bearing          fig. 2 - Boundary dimensions, thrust bearing

the bore diameter (d)
the outside diameter (D)
the width or height (B, C, T or H)
the chamfer dimensions (r)

ISThe boundary dimensions for metric bearings are standardized in the ISO general plans:

ISO 15 for radial rolling bearings, except insert bearings, some types of needle roller bearings and tapered roller bearings
ISO 104 for thrust bearings
ISO 355 for tapered roller bearings
Most rolling bearings follow ISO standard dimensions, which is a prerequisite to enable interchangeability.

The ISO general plan for radial bearings provides several series of standardized outside diameters for every standard bore diameter. They are called diameter series and are numbered 7, 8, 9, 0, 1, 2, 3 and 4 (in order of increasing outside diameter). Within each diameter series, different width series exist (width series 8, 0, 1, 2, 3, 4, 5 and 6 in order of increasing width). Fig. 3 shows diameter series 0, 2 and 3 combined with width series 0, 1, 2 and 3.

                                                              Fig. 3 - System of ISO dimension series

For thrust bearings, height series are used instead of width series. Height series are numbered 7, 9, 1 and 2.
Bearings to ISO general plans have the same boundary dimensions when they share the same bore diameter and dimension series (fig. 4). If not, they have different boundary dimensions.

Same bore diameter and dimension series                    Same bore diameter, but different dimension series

Deep groove ball bearing 6205 Cylindrical roller bearing NU 205 Cylindrical roller bearing NU 2205 ECP Angular contact ball bearing 3205 A

Dimension series 02        Dimension series 02          Dimension series 22                   Dimension series 32

                                         fig. 4 - Examples of boundary dimensions

Bearings with inch dimensions

In addition to the bearings in accordance with ISO dimensions, We has a comprehensive assortment of bearings with inch dimensions following American and British standards.