**SKF Bearing Type Base Code Analysis**
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Source: China Bearing Network | Date: December 16, 2013
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Understanding the base code of SKF bearings is essential for identifying and selecting the correct bearing housing. A spare bearing code typically consists of a base code combined with one or more supplementary codes. The **base code** identifies the type of bearing housing, its basic design, and outer dimensions. The **supplementary code**, on the other hand, refers to variations in structure or characteristics that differ from the base model.
The **SKF base code** usually contains three, four, or five digits, sometimes including letters. The first digit or letter indicates the housing type. The first two digits define the ISO series, where the first digit represents the width or height series (identified as B, T, or H), and the second digit indicates the diameter series (D). The last two digits of the base code represent the housing size code, which when multiplied by 5 gives the inner diameter in millimeters. However, there are some exceptions:
1. In some cases, the housing type and series number may be omitted. For example: 6(0)208-2Z (0)3209 A.
2. For bearings with an inner diameter of 10 mm or larger, or over 500 mm, the inner diameter is often directly indicated in millimeters without a code. For example: 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 inner diameters below 10 mm, such as deep groove, self-aligning, or angular contact ball bearings, the inner diameter is shown directly in millimeters without a code. For example: 629 or 129 (d = 9 mm).
5. Bearings with non-standard inner diameters are not coded but instead marked with up to three decimal places. These are separated by a slash from the base code. For example: 6202/15,875 (d = 15.875 mm).
Here are some common SKF bearing housing types:
- **Class 0**: Double-row angular contact ball bearing housing (often omitted). Example: (0)3204 A.
- **Class 1**: Self-aligning ball bearing housing. 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 housing. Example: 4206 ATN9.
- **Class 5**: Thrust ball bearing housing. Example: 51100.
- **Class 6**: Deep groove ball bearing housing. Example: 6213-2Z.
- **Class 7**: Angular contact ball bearing housing. Example: 7305 BECBM.
- **Class 8**: Cylindrical roller thrust bearing housing. Example: 81111 TN.
- **Class N**: Cylindrical roller bearing. Letters like NJ, NU, NUP indicate flange structures. Multi-row cylindrical roller bearings use NN. Example: NU 2317 ECJ.
- **Class C**: CARB bearing housing. Example: C 2205.
- **QJ Class**: Four-point contact ball bearing housing. Example: QJ 217 MA.
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This article is sourced from [China Bearing Network](http://www.chinabearing.net).
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Gully Gratings
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