All SKF standard bearings have a characteristic basic designation, which generally consists of 3, 4 or 5 figures, or a combination of letters and figures. The design of the system used for almost all standard ball and roller bearing types is shown schematically in diagram 1. The figures and combinations of letters and figures have the following meaning:
- The first figure or the first letter or combination of letters identifies the bearing type; the actual bearing type can be seen from the presentation (diagram 2).
- The following two figures identify the ISO Dimension Series; the first figure indicates the Width or Height Series (dimensions B, T or H respectively) and the second the Diameter Series (dimension D).
- The last two figures of the basic designation give the size code of the bearing; when multiplied by 5, the bore diameter in millimetres is obtained.
But there is no rule without some exceptions. The most important ones in the bearing designation system are listed below.
- In a few cases the figure for the bearing type and/or the first figure of the Dimension Series identification is omitted. These figures are given in brackets in diagram 3.
For bearings having a bore diameter smaller than 10 mm or equal to or greater than 500 mm, the bore diameter is generally given in millimetres and is not coded. The size identification is separated from the rest of the bearing designation by an oblique stroke, e.g. 618/8 (d = 8 mm) or 511/530 (d = 530 mm).
This is also true of standard bearings according to ISO 15:1998 that have bore diameters of 22, 28 or 32 mm, e.g. 62/22 (d = 22 mm).
Bearings with bore diameters of 10, 12, 15 and 17 mm have the following size code identifications:
00 = 10 mm
01 = 12 mm
02 = 15 mm
03 = 17 mm
- For some smaller bearings having a bore diameter below 10 mm, such as deep groove, self-aligning and angular contact ball bearings, the bore diameter is also given in millimetres (uncoded) but is not separated from the series designation by an oblique stroke, e.g. 629 or 129 (d = 9 mm).
- Bore diameters that deviate from the standard bore diameter of a bearing have always been given uncoded, in millimetres with up to three decimal places. This bore diameter identification is part of the basic designation and is separated from the basic designation by an oblique stroke, e.g. 6202/15.875 (d = 15,875 mm = 5/8 in).
Each standard bearing belongs to a given bearing series, which is identified by the basic designation without the size identification. Series designations often include a suffix A, B, C, D or E or a combination of these letters e.g. CA. These are used to identify differences in internal design, e.g. contact angle.
The most common series designations are shown in diagram 4 above the bearing sketches. The figures in brackets are not included in the series designation.