How to read a bearing number: 6204 2RS C3, decoded
The numbers stamped on a bearing tell you its type, size, seals and clearance. Here is how to read them, so you order the right part the first time.
Every bearing that comes across our counter carries a code on its face. It looks cryptic, but it follows a pattern that is shared, with small variations, by SKF, FAG, NTN, NSK, KOYO and most other makers. Once you can read it, you can tell the type, the exact size and the options at a glance.
We will use the most common bearing in the shop as our example: 6204 2RS C3.
1. The basic number: type, series and bore
The first part, 6204, is the basic designation.
- 6: the bearing type. 6 means a single-row deep groove ball bearing.
- 2: the dimension series. For the same bore, a higher number means a bigger, stronger bearing.
- 04: the bore code. From 04 upwards, multiply by 5 to get the bore in millimetres: 04 × 5 = 20 mm.
So a 6204 is a deep groove ball bearing with a 20 mm bore, and its catalogue size is 20 × 47 × 14 mm (bore × outside diameter × width).
Common type prefixes
| Starts with | Bearing type | Example |
|---|---|---|
6 |
Deep groove ball | 6204 |
7 |
Single-row angular contact ball | 7205 |
32 / 33 (4 digits) |
Double-row angular contact ball | 3205 |
1 |
Self-aligning ball | 1205 |
2 (5 digits) |
Spherical roller | 22208 |
3 (5 digits) |
Tapered roller | 30205 |
N, NU, NJ, NUP |
Cylindrical roller | NU 208 |
5 |
Thrust ball | 51106 |
29 |
Spherical roller thrust | 29416 |
Light, medium or heavy
The series digit changes the outside diameter and width while the bore stays the same. With a 20 mm bore:
- 6004: 20 × 42 × 12 mm (extra light)
- 6204: 20 × 47 × 14 mm (light)
- 6304: 20 × 52 × 15 mm (medium)
They all fit the same shaft, but only one will fit your housing. Never substitute a different series without checking the housing bore.
The small bores: 00 to 03, and under 10 mm
The first four bore codes do not follow the × 5 rule:
00= 10 mm,01= 12 mm,02= 15 mm,03= 17 mm- For bores under 10 mm, the last digit is the bore: a 608 has an 8 mm bore, a 626 a 6 mm bore.
- Sizes that fall between the steps are written with a slash: 62/22 has a 22 mm bore.
2. The suffixes: seals, clearance and cage
Everything after the basic number describes options. These are the ones you will see most often:
| Suffix | Meaning |
|---|---|
Z / ZZ / 2Z |
Metal shield on one side / both sides |
RS / 2RS |
Rubber contact seal on one side / both sides |
C3 |
Internal clearance larger than normal (common in motors) |
C2 |
Internal clearance smaller than normal |
N / NR |
Snap-ring groove / groove with snap ring fitted |
K |
Tapered bore (1:12), used with an adapter sleeve |
M, J, TN9 |
Cage type: machined brass, pressed steel, glass-fibre reinforced polyamide |
P6, P5, P4 |
Precision class, tighter than the normal P0 |
Each maker spells the seal suffix a little differently. A sealed 6204 is a 6204-2RS1 at SKF, 6204-2RSR at FAG, 6204DDU at NSK and 6204LLU at NTN, but they are the same basic bearing.
3. Putting it together
6204 2RS C3 = deep groove ball bearing, light series, 20 mm bore (20 × 47 × 14 mm), rubber-sealed on both sides, with C3 clearance.
A bigger example from our shelves: 22208 E1XL (FAG) = spherical roller bearing, 222 series, 40 mm bore (40 × 80 × 23 mm). E1 is FAG’s reinforced internal design and XL marks its X-life grade.
Cannot read the markings?
Worn or rusted bearings often lose their markings. That is fine. Measure the bore, outside diameter and width, or send us a photo on WhatsApp, and we will identify it for you. We also cross-reference numbers between brands and to replacements for discontinued parts.