Manufacturers and users of rolling bearings are, for reasons of price, quality and ease of replacement, only interested in a limited number of bearing sizes. The International Organization for Standardization (ISO) has therefore laid down General Plans for the boundary dimensions of
- metric radial rolling bearings in standard ISO 15:1998, except tapered roller bearings
- metric radial tapered roller bearings in standard ISO 355:1977
- metric thrust rolling bearings in standard ISO 104:2002.
ISO General Plans
The ISO General Plans for boundary dimensions of radial bearings contain a progressive series of standardized outside diameters for every standard bore diameter arranged in Diameter Series 7, 8, 9, 0, 1, 2, 3 and 4 (in order of increasing outside diameter). Within each Diameter Series different Width Series have also been established (Width Series 8, 0, 1, 2, 3, 4, 5, 6 and 7 in order of increasing width). The Width Series for radial bearings corresponds to the Height Series for thrust bearings (Height Series 7, 9, 1 and 2 in order of increasing height)
By combining a Width or Height Series with a Diameter Series, a Dimension Series, designated by two figures, is arrived at. The first figure identifies the Width or Height Series and the second the Diameter Series (fig 1).
In the ISO General Plan for single row metric tapered roller bearings, the boundary dimensions are grouped for certain ranges of the contact angle α, known as the Angle Series (Angle Series 2, 3, 4, 5, 6 and 7 in order of increasing angle). Based on the relationship between the outside and bore diameters, and between the total bearing width and the cross-sectional height, Diameter and Width Series have also been established. Here, a Dimension Series is obtained by combining the Angle Series with a Diameter and a Width Series (fig 2). These Dimension Series consist of one figure for the Angle Series and two letters, where the first letter identifies the Diameter Series and the second the Width Series.
With a very few exceptions, dictated by rolling bearing development, the bearings in this catalogue comply with the ISO General Plans or with other ISO standards for the dimensions of some bearing types for which the ISO Dimension Series are inappropriate. Relating to their principal dimensions, these bearings are interchangeable. Additional information is provided under the heading "Dimensions" in the introductory texts to the individual product sections.
Experience has shown that the requirements of the vast majority of bearing applications can be met using bearings with these standardized dimensions.
General Plans for inch bearings
A large group of bearings in inch sizes are inch tapered roller bearings. The dimensions of these bearings conform to AFBMA Standard 19-1974 (ANSI B3.19-1975). ANSI/ABMA Standard 19.2-1994 has subsequently replaced this standard, but this later standard no longer includes dimensions.
In addition to the inch tapered roller bearings, some inch ball bearings and cylindrical roller bearings that follow the earlier British Standard BS292-2:1982, are also available, but not shown in this catalogue. This standard has subsequently been withdrawn as a consequence of metrication and it is not recommended that these bearings be used for new designs.
Bearings identified by Drawing Numbers
Drawing Number bearings usually have customized dimensions, although frequently the difference between a Drawing Number bearing and a standard bearing lies in the internal design or a modified chamfer, for example. In some cases, e.g. multi-row roller bearings for rolling mills, the dimensions have become a standard for the industry, so that again, interchangeability is assured.