Bearing number decoder
Bearing number decoder: what the letters mean
Type the number from your bearing, such as 6204-2RS1/C3, and see what the type, bore, seals, clearance and cage letters mean.
Try:
How a bearing number is built
A number has three parts: the basic number (the type, series and bore), then letters for seals and clearance. In 6204-2RS1/C3, 6204 is the basic number, -2RS1 means rubber seals on both sides and /C3 means more internal clearance than normal. How to read a bearing number.
Finding the bore from the last two digits
For most bearings with a four or five digit number, multiply the last two digits by 5 to get the bore in mm: 04 is 20 mm, 05 is 25 mm, 16 is 80 mm. The exceptions are 00 (10 mm), 01 (12 mm), 02 (15 mm) and 03 (17 mm). Three digit numbers that start with 6, such as 608 and 623, are miniature bearings, where the last digit is the bore in mm.
The decoder uses these rules and the list of letters below. Makers sometimes use their own letters for the same feature, so if a letter is not in our list we say so instead of guessing.
Letters we explain
Shields and seals
Written after a hyphen or a space: 6204-2RS, 6204 ZZ.
| Letters | Meaning |
|---|---|
| 2Z | Metal shields on both sides (non-contact). Greased for life. |
| ZZ | Metal shields on both sides (non-contact). Greased for life. The same as 2Z. SKF writes it 2Z, other makers ZZ. |
| Z | A metal shield on one side only. |
| 2RS1 | Rubber contact seals on both sides. SKF’s earlier seal design. |
| 2RSH | Rubber contact seals on both sides. SKF’s current seal design in many sizes. |
| 2RSL | Low-friction rubber seals on both sides. SKF. |
| 2RS | Rubber contact seals on both sides. The same as 2RS1 and 2RSH, written differently by each maker. |
| RS1 | A rubber contact seal on one side only. SKF. |
| RSH | A rubber contact seal on one side only. SKF. |
| RS | A rubber contact seal on one side only. |
| DDU | Rubber contact seals on both sides. NSK’s way of writing 2RS. |
| LLU | Rubber contact seals on both sides. NTN’s way of writing 2RS. |
Internal clearance
Usually written after a slash: 6204/C3.
| Letters | Meaning |
|---|---|
| C2 | Internal clearance smaller than normal. |
| CN | Normal internal clearance. Usually not written on the bearing. |
| C3 | Internal clearance greater than normal. The usual choice for electric motors, because the bearing warms up in use. |
| C4 | Internal clearance greater than C3, for large temperature differences or heavy interference fits. |
| C5 | Internal clearance greater than C4. |
| CM | A clearance range for electric motor bearings. NSK’s own range. If your old bearing says CM, tell us. |
Accuracy (tolerance class)
Normal bearings are not marked. Higher classes cost more.
| Letters | Meaning |
|---|---|
| P6 | Dimensional and running accuracy tighter than normal. ISO tolerance class. |
| P5 | Higher running accuracy than P6, for machine tool spindles and similar. ISO tolerance class. |
| P4 | Very high running accuracy, higher than P5. ISO tolerance class. |
Cage
The cage keeps the balls or rollers evenly spaced.
| Letters | Meaning |
|---|---|
| TN9 | Glass-fibre reinforced polyamide cage. SKF. |
| J | Pressed steel cage. Letters for cages differ between makers. |
| M | Machined brass cage. Letters for cages differ between makers. |
Tapered bore
For bearings fitted on a sleeve or a tapered shaft.
| Letters | Meaning |
|---|---|
| K30 | Tapered bore, 1:30. Used on some large roller bearings. |
| K | Tapered bore, 1:12, for mounting on an adapter or withdrawal sleeve. |
Ring features
| Letters | Meaning |
|---|---|
| NR | Groove in the outer ring with a snap ring fitted. |
| N | Groove in the outer ring for a snap ring (the ring itself is separate). |
| W33 | Lubrication groove and holes in the outer ring (spherical roller bearings). |
Contact angle
| Letters | Meaning |
|---|---|
| B | Contact angle of 40°, on angular contact ball bearings such as 7205 B. Lets the bearing carry more axial load. |
Internal design
| Letters | Meaning |
|---|---|
| E | Optimised internal design with a higher load rating. SKF and FAG; other makers use other letters. |
Cylindrical roller bearing designs
| Letters | Meaning |
|---|---|
| NUP | Cylindrical roller bearing. Two ribs on the outer ring and one rib plus a loose rib on the inner ring, so it holds the shaft in both axial directions. |
| NU | Cylindrical roller bearing. Two ribs on the outer ring, none on the inner ring, so the shaft can move along its length. Cannot take axial load. |
| NJ | Cylindrical roller bearing. Two ribs on the outer ring and one on the inner ring, so it holds the shaft in one axial direction. |
| N | Cylindrical roller bearing. Two ribs on the inner ring, none on the outer ring, so the shaft can move along its length. |
Still not sure?
Send us the full number from the ring, or a photo of the old bearing, and we will tell you what it is and quote the right one.
Updated
Have a part number, or just a worn-out bearing?
Send it to us. We will tell you what it is, what it costs, and how soon it can be at your door.