Bearing Designation System: How to Read Any Part Number
A bearing part number has three layers: a shared ISO base (type + dimension series + bore code), then manufacturer-specific suffixes for seals, clearance, and precision. Learn the base once. Treat the suffixes as a lookup per brand.
Every bearing explainer on the web pretends one system covers all manufacturers. It doesn't. The ISO 15 base is shared, but the suffix layer is chaos. SKF's 2RS1 is NSK's DDU is FAG's 2RSR. Same bearing. Three different codes.
The part you actually need to read is the suffix. And no single table exists for it.
The three-layer structure
Every bearing number follows the same skeleton: optional prefix, basic designation, then one or more suffixes. The basic designation is ISO-standardized. The suffixes are not.
| Layer | What it tells you | Example from 6205-2RS1 |
|---|---|---|
| Prefix | Manufacturing variant (rare) | None |
| Basic designation | Type, dimensions, bore | 6205 |
| Suffix | Seals, clearance, precision | 2RS1 |
The basic designation is the part you can trust across brands. A 6205 from SKF has the same bore, OD, and width as a 6205 from NSK. Always. The suffix is where manufacturers diverge.
The basic designation decoded
The basic designation packs three pieces of information into a short string. Take 6205:
| Segment | Code | Meaning |
|---|---|---|
| Type code | 6 | Single row deep groove ball bearing |
| Dimension series | 2 | Diameter series 2, width series 0 (omitted) |
| Bore code | 05 | Bore = 05 × 5 = 25 mm |
Type codes follow ISO conventions. 6 = deep groove ball. 3 = tapered roller. 7 = angular contact ball. The dimension series encodes both width and diameter relative to bore. And the bore code uses the x5 rule: multiply by 5 to get millimeters.
But the x5 rule has exceptions for small bearings:
| Bore code | Bore diameter |
|---|---|
| 00 | 10 mm |
| 01 | 12 mm |
| 02 | 15 mm |
| 03 | 17 mm |
| 04+ | Code × 5 |
Bore code 05 means 25 mm. Bore code 08 means 40 mm. Simple math once you know the exception table.
Full decode: SKF 6205-2RS1
Part number: 6205-2RS1
| Segment | Code | Decoded value |
|---|---|---|
| Type | 6 | Deep groove ball bearing, single row |
| Dimension series | 2 | Diameter series 2, normal width |
| Bore code | 05 | 05 × 5 = 25 mm |
| Suffix | 2RS1 | Contact rubber seal, both sides (SKF) |
Physical dimensions: 25 mm bore × 52 mm OD × 15 mm width
The 2RS1 suffix is SKF-specific. It means molded rubber seals on both sides, contact type. Other manufacturers call this same configuration something different.
Suffix comparison across brands
This is where your spreadsheet gets messy. Four rows of the same 25 mm sealed bearing from four suppliers:
Raw supplier feed
- 6205-2RS1 (SKF)
- 6205DDU (NSK)
- 6205-2RSR (FAG)
- 6205-2RS (generic)
After normalization
- Type: Deep groove ball bearing
- Bore: 25 mm
- Seal: Contact rubber, both sides
- Clearance: CN (normal)
The suffix translation table you actually need:
| Seal/shield type | SKF | NSK | FAG |
|---|---|---|---|
| Contact rubber seal, both sides | 2RS1 | DDU | 2RSR |
| Non-contact shield, both sides | 2Z | ZZ | 2Z |
| Contact seal, one side | RS1 | DU | RSR |
Same physical product. Different suffix notation. Your PIM attribute should store the functional description, not the manufacturer code.
Second decode: Timken 32208
Timken metric bearings follow ISO 355 for tapered rollers. Different type-code logic, same bore-code math.
| Segment | Code | Meaning |
|---|---|---|
| Type | 3 | Tapered roller bearing |
| Dimension series | 22 | ISO 355 series code |
| Bore code | 08 | 08 × 5 = 40 mm |
Physical dimensions: 40 mm bore × 80 mm OD × 24.75 mm width.
Imperial Timken bearings like LM67048 use a completely different system. Sequential alphanumeric codes, no bore math, separate cone and cup part numbers. Don't try to apply the x5 rule to them.
Clearance and precision suffixes
No suffix means normal. That's the key insight. Absence of a clearance code means CN (normal clearance). Absence of a precision code means P0 (standard tolerance).
Suffix starts with C + number: Clearance class. C3 is most common for industrial motors (greater than normal). C2 means less than normal.
Suffix starts with P + number: Precision class. P6 = ABEC 3. P5 = ABEC 5. P4 = ABEC 7.
Contains RS, Z, or seal-related letters: Seal or shield configuration. Look up per manufacturer.
Contains M, MA, TN: Cage material variant. Usually not critical for catalog normalization.
| Clearance progression | Precision progression |
|---|---|
| C2 < CN (normal) < C3 < C4 < C5 | P0 (ABEC 1) → P6 (ABEC 3) → P5 (ABEC 5) → P4 (ABEC 7) → P2 (ABEC 9) |
The base system is defined in ISO 15 (rolling bearing designations) and ISO 492 (tolerances). Manufacturer catalogs from SKF, NSK, and FAG publish their suffix conventions, though you'll need to cross-reference them yourself.
Normalizing bearing data in your PIM
- Confirm bore code math (x5 rule or exception table)
- Identify type code from first digit
- Look up seal suffix using manufacturer-specific table
- Flag C3/C4 clearance if present
- Flag precision class if not P0/standard
- Cross-reference on ISO base number for dimensional match
Matching the basic ISO number (6205) gives you dimensional compatibility. You still need to match the suffix to confirm functional equivalence. A 6205-2RS1 and a 6205ZZ have the same bore and OD, but different sealing. That matters for your customer's application.
AI classifiers that output ETIM feature values can parse the ISO base reliably. Suffix normalization still needs a per-brand lookup table. Build the table once. Reference it forever.