In the world of machinery, a bearing number is more than just a random string of digits and letters—it is the technical fingerprint of a critical component. Whether you are a maintenance technician facing an unexpected failure or a procurement specialist sourcing for a new project, understanding how to read and identify bearing numbers is essential. This knowledge ensures you select the correct part, avoid costly downtime, and maintain the integrity of your equipment. DUHUI will decode the seemingly complex system of bearing identification.
The Bearing Number Consists of: Prefix, Basic, and Suffix
Most rolling-element bearings from major manufacturers follow a structured designation system. While minor variations exist between companies like SKF, NSK, or FAG, the underlying logic is standardized by organizations like ISO . A typical bearing number is composed of three parts:
- Prefix: Indicates component parts or material variations.
- Basic Number: Describes the bearing type, series, and bore size.
- Suffix: Denotes design modifications like seals, cages, clearances, and precision classes.
Understanding this three-part structure is the first step toward accurate bearing identification.
Decoding the Basic Number
The basic number is the heart of the bearing identification. In a standard metric bearing, it usually consists of three to five digits.
The First Digit/Letter: Identifying the Bearing Type
The first character tells you what kind of bearing you are holding. This is the most critical piece of information.
| Code | Bearing Type | Typical Application |
| 6 | Single Row Deep Groove Ball Bearing | General machinery, electric motors, pumps |
| 7 | Single Row Angular Contact Ball Bearing | Machine tool spindles, gearboxes (supports combined loads) |
| 1 | Self-Aligning Ball Bearing | Applications with shaft misalignment |
| 2 | Spherical Roller Bearing | Heavy-duty industrial applications, vibrating equipment |
| 3 | Tapered Roller Bearing | Vehicle wheels, gearboxes (supports heavy radial and axial loads) |
| N | Cylindrical Roller Bearing | High-speed and high-radial-load applications |
The Second Digit: Determining the Dimension Series
The second digit indicates the dimension series, which refers to the robustness of the bearing cross-section. It defines the relationship between the bearing’s width and its outer diameter for a given bore size . For example, in a 62** series, the ‘2’ signifies a “Light” series, while 63** signifies a “Medium” series, which has a larger outer diameter and width to carry heavier loads .
The Last Two Digits: Calculating the Bore Size
For bearing bore diameters from 20 mm to 480 mm, the last two digits of the basic number, when multiplied by 5, give the exact bore diameter in millimeters .
Example: In bearing 6206, the last two digits are 06. 06 x 5 = 30 mm bore.
There are important exceptions for common smaller bores :
| Last Two Digits | Bore Diameter |
| 00 | 10 mm |
| 01 | 12 mm |
| 02 | 15 mm |
| 03 | 17 mm |
For bearings with a bore under 10 mm or over 500 mm, the diameter is usually given directly in millimeters and separated by a slash (e.g., 618/8 for an 8 mm bore) .
Understanding Prefixes
Prefixes are less common but provide essential information, often indicating that the part is a component of a bearing or made from a special material.
- Component Prefixes: L stands for a separable inner or outer ring (e.g., LNU207 is the inner ring of a NU207 bearing). R indicates a set of rollers with a cage (with or without a ring) .
- Material/Heat Treatment Prefixes: Manufacturers use codes like TS2 (NTN) to signify parts are heat-stabilized for high-temperature operation (up to 160°C), ensuring the bearing maintains its dimensions under heat .
Deciphering Suffixes
Suffixes are where bearings gain their specific performance characteristics. After you have identified the type and size, suffixes tell you how the bearing interacts with its environment.
Seals and Shields: These protect the bearing from contamination.
- RSR / 2RS: One or two-sided contact rubber seals (good contamination protection) .
- Z / ZZ: One or two-sided non-contact metal shields .
Internal Clearance: The amount of play inside the bearing.
- C3: Increased radial internal clearance. This is a common modification for applications where the bearing will experience temperature rise, allowing the inner ring to expand without preloading the bearing to failure .
- C4: Clearance greater than C3. CN (or no suffix) denotes normal clearance .
Cage (Retainer) Material: The cage separates the rolling elements.
- J: Pressed steel cage .
- M: Machined brass cage .
- T: Polymer cage .
Tolerance (Precision) Classes: Bearings manufactured to tighter dimensional and running accuracy.
- P6: Higher accuracy than standard (P0).
- P5: Precision class, common for machine tools.
- P4: Super precision class .
Other Common Modifications:
- K: Tapered bore (1:12 taper) for mounting on a tapered shaft sleeve .
- N: Snap ring groove in the outer ring .
Practical Steps to Identify Any Bearing Number
- Write Down the Entire Number: Note every letter and number, including spaces or slashes. A missing suffix could mean the wrong seal type.
- Decode the Basics: Use the rules above to identify the type, series, and bore size.
- Analyze the Suffixes: Match the letters to their meanings regarding seals, clearance, and precision. If a suffix is unfamiliar, proceed to step four.
- Consult Official Resources: While this guide covers the basics, manufacturers have unique codes. Always verify your findings with the official online catalog or technical manual of the brand you are using .
- Measure If Necessary: If the number is worn off, the bearing can still be identified by measuring the bore (d), outside diameter (D), and width (B). These three dimensions are often enough to pinpoint the exact basic number series .
Frequently Asked Questions
1. What do bearing numbers mean?
Bearing numbers are a coded system that identifies the bearing’s type, dimension series, and bore size. Supplementary letters (prefixes/suffixes) indicate design variations like seals, cage material, internal clearance, and precision grade .
2. How do I read bearing numbers?
Start from the left. The first digit/number tells you the bearing type (e.g., 6 = deep groove). The second digit indicates the series (strength). The last two digits, when multiplied by 5 (with exceptions for 00-03), give the bore size in millimeters. Any letters after the numbers are suffixes that describe special features .
3. What is a bearing trade number?
A trade number is essentially the standardized part number used across the industry. It allows for interchangeability between different manufacturers. A 6203-2RS bearing from SKF will have the same dimensions and basic features as a 6203-2RS from DUHUI .
4. What is a bearing part number breakdown?
A breakdown is the process of separating the bearing number into its constituent parts to understand each element. For example, breaking down 6206-2RS:
- 62 = Bearing series (Type 6, Series 2).
- 06 = Bore size (30mm).
- 2RS = Suffix meaning two rubber seals .
5. What is bearing identification?
Bearing identification is the complete process of determining all specifications of a bearing by reading its part number or, if the number is missing, by physically measuring its dimensions and observing its features (seals, cage type, etc.) .
6. What is the difference between bearing number systems used by SKF, NSK, FAG, and Chinese manufacturers?
Most global bearing manufacturers follow the ISO 15 standard for dimensional series (e.g., 6204, 6308), which ensures interchangeability of basic numbers. However, prefixes and suffixes vary by brand. For example, a sealed deep groove ball bearing may be labeled “6204-2RS” by SKF, “6204-2RS1” by NSK, and “6204-2RS” by many Chinese manufacturers – all meaning the same rubber seal on both sides. Prefixes like “F” (flanged) or “K” (tapered bore) are also similar across brands, but some proprietary codes (e.g., SKF’s “TN9” for PA66 cage) differ. Always cross-reference the suffix meaning from the manufacturer’s catalog. For dimensions and basic number, ISO standards guarantee compatibility.
7. How do I calculate the bore diameter from a bearing number when the number has only two digits after the type?
For metric bearings, the last two digits of the basic number (excluding prefixes/suffixes) give the bore:
- 00 = 10 mm
- 01 = 12 mm
- 02 = 15 mm
- 03 = 17 mm
- From 04 to 99, multiply the last two digits by 5 to get the bore in mm.
Example: 6204 → last two digits “04” → 4 × 5 = 20 mm bore.
Exception: For bearings with a bore diameter below 10 mm, the last digit directly represents the bore (e.g., 608 → 8 mm bore). Also, bearings with a single slash (e.g., 6204/22) have the bore indicated after the slash in mm.
8. What do the suffixes “C3”, “C4”, or “CN” mean in a bearing number?
These suffixes define internal radial clearance (the play inside the bearing).
- CN (or no suffix) = Normal clearance (standard for most applications).
- C2 = Smaller than normal clearance (for high precision, low vibration).
- C3 = Larger than normal clearance (for higher speeds, temperature differences).
- C4 = Larger than C3 (for extreme thermal expansion).
Choosing the wrong clearance can cause premature failure. For example, electric motors often use C3, while machine tool spindles use C2. Always check the original equipment specification.
9. How can I identify the seal or shield type from a bearing suffix?
Common suffixes for contact seals and shields:
- 2RS or 2RSH = Rubber seal on both sides (contact seal, good protection, higher torque).
- 2RZ = Low-friction rubber seal (non-contact, lower torque).
- ZZ or 2Z = Metal shield on both sides (non-contact, protects from large debris, higher speed).
- RS or RZ = Seal/shield on one side only (open on the other).
- Open (no suffix) = No seals or shields.
Example: 6304-2RS has two rubber seals; 6304-ZZ has two metal shields. For washdown or dusty environments, 2RS is preferred; for high-speed applications, ZZ or 2RZ.
10. Why does my bearing number have a letter “W” or “N” after the bore code – for example, 6204N?
These are suffixes that indicate special groove or snap ring features:
- N = Snap ring groove on the outer ring (but no snap ring included).
- NR = Snap ring groove with snap ring fitted.
- K = Tapered bore (1:12 taper, often used with adapter sleeves).
- W (in some European brands like FAG) = Stainless steel bearing (e.g., 6204-W).
- S or SO = Grease-filled sealed bearing (specific lubrication).
These features affect mounting and axial location. If you see “N” on a worn bearing, you need a snap ring groove for housing retention.
11. How do I read a bearing number if part of it is worn off or illegible?
Use a three-step method:
- Measure the bore (d), outer diameter (D), and width (B) with a caliper.
- Identify the bearing type by design (deep groove, angular contact, tapered roller, etc.).
- Cross-reference the dimensions with a bearing dimension table (e.g., ISO 15 for metric ball bearings).
For example, if you measure d=20 mm, D=47 mm, B=14 mm, that matches a 6204 deep groove ball bearing. If only the suffix is missing, check for seal remnants or snap ring groove. Many online tools let you input dimensions to find the standard bearing number.
12. What is the difference between a “6204” and a “6204-2Z” – and does it affect interchangeability?
The basic number “6204” defines the dimensions and load ratings. The suffix “2Z” (or ZZ) means two metal shields. A plain “6204” is open (no shields). They are dimensionally identical – same bore, OD, width – and can be mounted in the same housing. However, they are not functionally interchangeable because seals/shields change protection against contamination and maximum rotational speed (open bearings have higher speed limits). Always replace with the same seal/shield type unless the equipment design is modified.
Conclusion
Learning how to read and identify bearing numbers demystifies a process that is vital for any maintenance or engineering professional. The system, built on a logical foundation of type, size, and feature codes, provides all the information needed to select the perfect component for any application. By mastering these basics, you ensure accuracy, efficiency, and reliability in your operations. When you are ready to specify your next bearing, remember that DUHUI Bearing is here to deliver the quality and precision that the numbers on your list demand.
