How to Read a Bearing Number (Designation Explained)
A bearing number is not random — it encodes the bearing's type, its size and its features. Once you can read it, you can tell at a glance what a bearing is and what shaft it fits, without reaching for a catalogue. Most metric bearings follow the same pattern: an optional prefix, a basic number (type + size series + bore), and one or more suffixes.
Take 6205-2RS C3 as the example we'll decode:
Step 1 — The type (first character)
The first digit or letters tell you the bearing type. The most common codes:
| Code | Type |
|---|---|
| 6 | Single-row deep-groove ball (the most common) |
| 7 | Single-row angular-contact ball |
| 1 | Self-aligning ball |
| 2 | Spherical roller |
| 3 | Tapered roller |
| 5 | Thrust ball |
| N, NU, NJ… | Cylindrical roller |
So the 6 in 6205 means a deep-groove ball bearing.
Step 2 — The size (dimension) series
The next digit gives the dimension series — roughly, how heavy-duty the bearing is for a given bore. For the same shaft size, a higher series means a larger outside diameter and more load capacity. So a 6205 is lighter than a 6305, which is lighter than a 6405 — all with the same 25 mm bore. The 2 in 6205 is dimension series 2 (a medium, general-purpose section).
Step 3 — The bore (the last two digits)
This is the part most people actually want — the shaft size. For bore codes 04 and above, the rule is simple:
So 05 means 05 × 5 = 25 mm. The only exceptions are the four smallest standard codes, which have fixed values:
| Code | 00 | 01 | 02 | 03 | 04 and up |
|---|---|---|---|---|---|
| Bore | 10 mm | 12 mm | 15 mm | 17 mm | code × 5 |
Bores below 10 mm or above 480 mm follow special rules (often the bore appears directly, sometimes after a "/").
Step 4 — The suffixes (seals, clearance, more)
Anything after the basic number describes features. The common ones:
2RS/RS— two / one contact rubber seals.ZZ/Z— two / one metal shields (non-contact).C3— internal clearance greater than normal (C2, C4, C5 also exist).P6 / P5— higher precision class.Mbrass cage,TNnylon cage.
(See the full suffix decoder for the rest.)
Putting it together
6205-2RS C3 = deep-groove ball bearing · dimension series 2 · 25 mm bore · two contact seals · clearance greater than normal.
More worked examples
| Number | Meaning |
|---|---|
6000 | Deep-groove ball, light series 0, bore 10 mm. |
6204 | Deep-groove ball, series 2, bore 04 × 5 = 20 mm. |
6305 | Deep-groove ball, heavier series 3, bore 25 mm. |
7206 B | Angular-contact ball, series 2, bore 30 mm, 40° contact angle. |
NU 309 | Cylindrical roller, series 3, bore 09 × 5 = 45 mm. |
22210 | Spherical roller, dimension series 22, bore 10 × 5 = 50 mm. |
30205 | Tapered roller (3-series), bore 25 mm. |
A note on brands
The basic number (type, series, bore) is common across manufacturers, so a 6205 is a 6205 everywhere. The suffixes, however, differ between SKF, FAG, NSK, NTN and others — the same feature can be coded with different letters. When cross-referencing, match the function (seals, clearance, precision, cage), not just the letters. You can compare dimensions across brands with the bearing search.
Frequently asked questions
How do I find a bearing's bore size from its number?
Take the last two digits (the bore code) and multiply by 5 for codes 04 and above — so 6205 has a 25 mm bore. Codes 00, 01, 02, 03 mean 10, 12, 15 and 17 mm.
What does 6205 mean?
A single-row deep-groove ball bearing (6), dimension series 2, with a 25 mm bore (05 × 5).
Are bearing numbers the same across brands?
The basic number is, so the size and type match across makers. The suffix letters for seals, clearance and cages vary by manufacturer, so check those against the maker's catalogue.
For the complete reference, including the dimension-series detail and every suffix, see reading a bearing number in the Standards Hub.