6904 bearing dimensions
A 6904 bearing is 20 mm bore × 37 mm outside diameter × 9 mm wide (0.787 × 1.457 × 0.354 in). The sealed version is 6904-2RS; the shielded version is 6904-ZZ.
6904 at a glance
Boundary dimensions in millimetres and inches, and the common closure designations.
- Bore, d
- 20 mm 0.7874"
- Outside diameter, D
- 37 mm 1.4567"
- Width, B
- 9 mm 0.3543"
- Section height, (D − d)/2
- 8.5 mm 0.3346"
- Series
- 69 series thin-section
- Bore code
- 04 04 × 5 = 20 mm
- Sealed, both sides
- 6904-2RS
- Shielded, both sides
- 6904-ZZ
- Open
- 6904 no closures; any version may add C3 for extra internal clearance
Reading the number 6904
Every deep groove ball bearing number follows the same pattern: type, dimension series and bore code, then suffixes.
Seals, shields and suffixes
Suffixes add closures and internal clearance. They do not change the boundary dimensions: a sealed and an open bearing of the same number are interchangeable in size.
| Suffix | Meaning | 6904 example |
|---|---|---|
| Open (no suffix) | No seals or shields. Can be relubricated, or run in an oil bath; the housing needs its own seal against dirt. | 6904 |
| Z | One metal shield, on one side only. | 6904-Z |
| ZZ, 2Z | Metal shields on both sides. Non-contact, so low friction; keeps out larger dirt. Usually greased for life. | 6904-ZZ |
| RS | One rubber contact seal, on one side only. | 6904-RS |
| 2RS, 2RS1, 2RSH, 2RSR, DDU, LLU | Rubber contact seals on both sides. Better than shields against fine dirt and splashing water, with a little more friction. Usually greased for life. | 6904-2RS |
| C3 | Radial internal clearance greater than normal (CN). Used with tight shaft or housing fits, or where the inner ring runs hotter than the outer ring. | 6904-2RS C3 |
6904 in other brands
The sealed and shielded versions as each maker writes them. All share the same boundary dimensions.
| Maker | Sealed both sides | Shielded both sides |
|---|---|---|
| SKF | 6904-2RSH | 6904-2Z |
| FAG (Schaeffler) | 6904-2RSR | 6904-2ZR |
| NSK | 6904DDU | 6904ZZ |
| NTN | 6904LLU | 6904ZZ |
| Koyo (JTEKT) | 6904-2RS | 6904ZZ |
| Timken | 6904-2RS | see catalogue |
Seal designs and suffixes vary by maker, size range and product generation, for example contact versus low-friction seals. Confirm the exact designation in the maker's catalogue before ordering.
Same 20 mm bore, other series
Bearings that fit the same shaft. A heavier series carries more load in a bigger housing bore; a thin-section series saves space and weight.
69 series
Common questions
What size is a 6904 bearing?
20 mm bore, 37 mm outside diameter and 9 mm wide, which is 0.787 × 1.457 × 0.354 in.
What does 2RS mean on a 6904 bearing?
6904-2RS has rubber contact seals on both sides. 6904-ZZ (also written 6904-2Z) has metal shields on both sides. Both have the same 20 × 37 × 9 mm dimensions.
Is 6904-2RS the same as 6904-ZZ?
They are the same size and interchangeable in a housing. The sealed 6904-2RS keeps out fine dirt and water better; the shielded 6904-ZZ runs with less friction.
What is the SKF equivalent of 6904-2RS?
SKF writes it 6904-2RSH; FAG 6904-2RSR, NSK 6904DDU, NTN 6904LLU and Koyo 6904-2RS. Check the maker's catalogue for the exact seal type.
What does the number 6904 mean?
6 is the deep groove ball bearing type, 9 is the thin-section dimension series, and 04 × 5 = 20 mm (from 04 up, multiply by 5).
Which bearings have the same bore as 6904?
6804, 6004, 6204, 6304 also have a 20 mm bore, with different outside diameters and widths.