6311 bearing dimensions
A 6311 bearing is 55 mm bore × 120 mm outside diameter × 29 mm wide (2.165 × 4.724 × 1.142 in). The sealed version is 6311-2RS; the shielded version is 6311-ZZ.
6311 at a glance
Boundary dimensions in millimetres and inches, and the common closure designations.
- Bore, d
- 55 mm 2.1654"
- Outside diameter, D
- 120 mm 4.7244"
- Width, B
- 29 mm 1.1417"
- Section height, (D − d)/2
- 32.5 mm 1.2795"
- Series
- 63 series medium
- Bore code
- 11 11 × 5 = 55 mm
- Sealed, both sides
- 6311-2RS
- Shielded, both sides
- 6311-ZZ
- Open
- 6311 no closures; any version may add C3 for extra internal clearance
Reading the number 6311
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 | 6311 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. | 6311 |
| Z | One metal shield, on one side only. | 6311-Z |
| ZZ, 2Z | Metal shields on both sides. Non-contact, so low friction; keeps out larger dirt. Usually greased for life. | 6311-ZZ |
| RS | One rubber contact seal, on one side only. | 6311-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. | 6311-2RS |
| 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. | 6311-2RS C3 |
6311 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 | 6311-2RSH | 6311-2Z |
| FAG (Schaeffler) | 6311-2RSR | 6311-2ZR |
| NSK | 6311DDU | 6311ZZ |
| NTN | 6311LLU | 6311ZZ |
| Koyo (JTEKT) | 6311-2RS | 6311ZZ |
| Timken | 6311-2RS | 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 55 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.
63 series
Common questions
What size is a 6311 bearing?
55 mm bore, 120 mm outside diameter and 29 mm wide, which is 2.165 × 4.724 × 1.142 in.
What does 2RS mean on a 6311 bearing?
6311-2RS has rubber contact seals on both sides. 6311-ZZ (also written 6311-2Z) has metal shields on both sides. Both have the same 55 × 120 × 29 mm dimensions.
Is 6311-2RS the same as 6311-ZZ?
They are the same size and interchangeable in a housing. The sealed 6311-2RS keeps out fine dirt and water better; the shielded 6311-ZZ runs with less friction.
What is the SKF equivalent of 6311-2RS?
SKF writes it 6311-2RSH; FAG 6311-2RSR, NSK 6311DDU, NTN 6311LLU and Koyo 6311-2RS. Check the maker's catalogue for the exact seal type.
What does the number 6311 mean?
6 is the deep groove ball bearing type, 3 is the medium dimension series, and 11 × 5 = 55 mm (from 04 up, multiply by 5).
Which bearings have the same bore as 6311?
6011, 6211 also have a 55 mm bore, with different outside diameters and widths.