**SKF Bearing Type Base Code Analysis**
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Source: China Bearing Network | Date: December 16, 2013
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The spare bearing code is composed of a base code and one or more supplementary codes. The base code identifies the type of bearing housing, its basic design, and outer dimensions. The supplementary code refers to variations in structure or other characteristics that differ from the base.
For SKF bearings, the base code typically consists of three, four, or five digits, or a combination of letters and numbers. The first digit or letter indicates the housing type. The first two digits determine the ISO series, with the first digit representing the width or height series (B, T, or H), and the second digit indicating the diameter series (D). The last two digits represent the size code, which when multiplied by 5 gives the inner diameter in millimeters.
However, there are several exceptions:
1. In some cases, the housing type and the first digit of the series may be omitted. For example: 6(0)208-2Z (0)3209 A.
2. For SKF housings with an inner diameter of 10 mm or more, or 500 mm or more, the inner diameter is often directly indicated in millimeters without a code. Other parts of the housing type are separated by a slash, such as 618/8 (d = 8 mm) or 618/530 MA (d = 530 mm).
3. Bearings with inner diameters of 10, 12, 15, and 17 mm are marked with specific codes: 00 = 10 mm, 01 = 12 mm, 02 = 15 mm, 03 = 17 mm.
4. For small bearings with an inner diameter less than 10 mm, such as deep groove, self-aligning, and angular contact ball bearings, the inner diameter is also indicated in millimeters but not separated by a slash. For example: 629 or 129 (d = 9 mm).
5. If the inner diameter deviates from the standard, it is shown using up to three decimal places. This is part of the base code and separated by a slash, such as 6202/15,875 (d = 15.875 mm).
Different categories of SKF housing types include:
- **Class 0**: Double-row angular contact ball bearing housing (often omitted). Example: (0)3204 A
- **Class 1**: Self-aligning ball bearing seat. Example: 1201 ETN9
- **Class 2**: Spherical roller bearing housing. Example: 22209 E, 29328 E
- **Class 3**: Tapered roller bearing housing. Example: 32016 X/Q
- **Class 4**: Double-row deep groove ball bearing seat. Example: 4206 ATN9
- **Class 5**: Thrust ball bearing seat. Example: 51100
- **Class 6**: Deep groove ball bearing seat. Example: 6213-2Z
- **Class 7**: Angular contact ball bearing seat. Example: 7305 BECBM
- **Class 8**: Cylindrical roller thrust bearing seat. Example: 81111 TN
- **Class N**: Second letter of cylindrical roller bearings, sometimes divided into the third letter, used to define the flange structure. Example: NJ, NU, NUP. Double or multi-row cylindrical roller bearings are always denoted with NN. Example: NU 2317 ECJ
- **Class C**: CARB bearing housing. Example: C 2205
- **QJ Class**: Four-point contact ball bearing seat. Example: QJ 217 MA
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**Related Bearing Knowledge**
- Common terminology and definition of one-way bearing thrust bearing
- Understanding the working principle of bearing heaters after IKO bearing equipment
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