How to read a bearing number
Every digit and letter in a bearing number tells you something. Here is how to decode one in under a minute.
Most bearings follow the ISO numbering system, so the number stamped on the ring tells you the type and size no matter who made it. A standard number has three parts: type, series and bore code, followed by optional suffixes.
1. The first digit: bearing type
| First digit / letters | Bearing type |
|---|---|
| 6 | Single row deep groove ball bearing |
| 3 | Taper roller bearing |
| 5 | Thrust ball bearing |
| N, NU, NJ, NUP, NF | Cylindrical roller bearing |
| QJ | Four point contact ball bearing |
| 2 | Spherical roller bearing (22xxx series) |
| 1 | Self-aligning ball bearing |
| 7 | Angular contact ball bearing |
2. The middle digit(s): series
The next digit (or two) shows how heavy the bearing is for its bore. For ball bearings: 60xx is extra light, 62xx is light, 63xx is medium. A 6205, 6305 and 6005 all have a 25 mm bore, but the 6305 is the biggest and strongest.
3. The last two digits: bore size
The last two digits give the inner diameter (bore):
- 00 = 10 mm
- 01 = 12 mm
- 02 = 15 mm
- 03 = 17 mm
- 04 and above: multiply by 5. So 04 = 20 mm, 05 = 25 mm, 10 = 50 mm, 20 = 100 mm.
4. Suffixes: seals, shields and more
| Suffix | Meaning |
|---|---|
| ZZ / 2Z | Metal shields on both sides |
| Z | Metal shield on one side |
| 2RS / 2RS1 / LLU / DDU | Rubber seals on both sides (names differ by maker) |
| RS | Rubber seal on one side |
| N | Snap ring groove in the outer ring |
| NR | Snap ring groove with the snap ring fitted |
| C3 | Internal clearance larger than normal, for hot running or tight fits (common in motors) |
| M / brass | Brass (machined) cage |
Worked examples
- 6205 2RS: 6 = deep groove ball, 2 = light series, 05 = 25 mm bore, 2RS = rubber sealed both sides. Size 25 x 52 x 15 mm.
- 6303 ZZ: deep groove ball, medium series, 03 = 17 mm bore, metal shields. Size 17 x 47 x 14 mm.
- 30205: 3 = taper roller, 02 = light series, 05 = 25 mm bore. Size 25 x 52 x 16.25 mm.
- 51107: 5 = thrust ball, 11 = light series, 07 = 35 mm bore. Size 35 x 52 x 12 mm.
Inch taper bearings are different
Many taper bearings in Indian trucks and imported vehicles use inch-based cone and cup numbers, written as two numbers with a slash, for example 25580/20 or 3782/20. The first number is the cone, the second is the cup. These numbers do not follow the bore code rule above, so always read both numbers from the old bearing.
Frequently asked questions
What does the 05 in 6205 mean?
From 04 upwards, multiply the last two digits by 5 to get the bore in mm. 05 x 5 = 25 mm.
Is 6205 2RS the same as 6205 2RS1 or 6205 LLU?
Yes, the size is the same. 2RS1 and LLU are other makers' names for a bearing with rubber seals on both sides.
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