Standardized boundary dimensions

Boundary dimensions are the main dimensions of a bearing (fig. 1 and fig. 2). They comprise:
  • the bore diameter (d)
  • the outside diameter (D)
  • the width or height (B, C, T or H)
  • the chamfer dimensions (r)

The boundary dimensions for metric bearings are standardized in the ISO2) general plans:

  • ISO 15 for radial rolling bearings, except Y-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.

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.

Bearings with inch dimensions

In addition to the bearings in accordance with ISO dimensions, SKF has a comprehensive assortment of bearings with inch dimensions following American and British standards.
  1. 1)ISO uses T.
  2. 2)For details on how to obtain relevant ISO documentation, refer to ISO - International Organisation for Standardization.
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