6311 bearing: complete specifications & equivalents
The 6311 is a ISO 15 radial bearing sized 55 x 120 x 29 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 55 mm |
| Outer diameter D | 120 mm |
| Width B | 29 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN / C3 available |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 74.1 kN |
| Basic static load rating C0 | 45 kN |
| Fatigue load limit Pu | 1.9 kN |
| Reference speed (thermal) | 12000 rpm |
| Limiting speed (mechanical) | 8000 rpm |
| Operating temperature | -40 to +150 °C |
| Mass | 1350 g |
| Manufacturer designation | SKF 6311 |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018) |
| Last verified | 2026-09-25 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018)) · extracted 2026-09-24
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018)); SKF® and SKF Explorer® are trademarks of AB SKF, used here for identification only — mpnbase is not an authorized SKF distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at skf.com.
Dimensions in inches & 6300-series range
| Bore d | 2.165 in |
|---|---|
| Outer diameter D | 4.724 in |
| Width B | 1.142 in |
| ISO bore code | 11 |
| Radial section height (D−d)/2 | 32.5 mm |
| Smallest bore in 6300-series | 2 mm |
| Largest outer diameter in 6300-series | 500 mm |
| Width range across 6300-series | 3–95 mm |
| Bore position in 6300-series (smallest first) | 18 of 40 |
| Bore above smallest 6300-series size | 53 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 6311-2RS-FAG | FAG | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 55×120×29 mm envelope per ISO 15; seal variant (OPEN vs 2RS) and load ratings differ — confirm sealing and rating before substituting. |
| 6311-FAG | FAG | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 55×120×29 mm envelope per ISO 15; catalogue load ratings differ by >10% — re-rate the application before substituting. |
| 6311-ZZ-FAG | FAG | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 55×120×29 mm envelope per ISO 15; seal variant (OPEN vs ZZ) and load ratings differ — confirm sealing and rating before substituting. |
| 6311 | ISO 15 | full Dimensions and internal design equivalent — standard interchange. | ISO 15 boundary-dimension envelope; standard interchange — confirm clearance class and precision with the supplier. |
| 6311-2RS-NSK | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 55×120×29 mm envelope per ISO 15; seal variant differs (OPEN vs 2RS) — confirm sealing suits the duty. |
| 6311-NSK | NSK | full Dimensions and internal design equivalent — standard interchange. | Identical ISO 15 envelope, seal and ratings band — standard interchange; re-verify precision class and clearance per supplier. |
| 6311-RSR | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 55×120×29 mm envelope per ISO 15; seal variant differs (OPEN vs RSR) — confirm sealing suits the duty. |
| 6311-ZZ-NSK | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 55×120×29 mm envelope per ISO 15; seal variant differs (OPEN vs ZZ) — confirm sealing suits the duty. |
| 6311-2RS-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 55×120×29 mm envelope per ISO 15; seal variant differs (OPEN vs 2RS) — confirm sealing suits the duty. |
| 6311-NTN | NTN | full Dimensions and internal design equivalent — standard interchange. | Identical ISO 15 envelope, seal and ratings band — standard interchange; re-verify precision class and clearance per supplier. |
| 6311-RSR-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 55×120×29 mm envelope per ISO 15; seal variant differs (OPEN vs RSR) — confirm sealing suits the duty. |
| 6311-ZZ-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 55×120×29 mm envelope per ISO 15; seal variant differs (OPEN vs ZZ) — confirm sealing suits the duty. |
| 7311 | SKF | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | — |
| NU311 | SKF | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | — |
| 21311 | SKF | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | — |
| 6311-M | SKF | full Dimensions and internal design equivalent — standard interchange. | SKF 6311 M (machined brass cage, open arrangement) is the same-size execution on the 55×120×29 mm envelope with ratings within 10 % — boundary dimensions interchangeable. |
| 311 | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | SKF 311 shares the 55×120×29 mm envelope but catalogue C/C0 differ — envelope match only after a load check. |
| 311-ZZ | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | SKF 311-2Z shares the 55×120×29 mm envelope but catalogue C/C0 differ — envelope match only after a load check. |
Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.
How the 6311 model number is decoded
In the 6300-series (diameter series 3 of ISO 15) the last two digits encode the bore: 6311 carries bore code 11 = 55 mm. Outside diameter 120 mm and width 29 mm come from the ISO 15 boundary-dimensions general plan. With no seal suffix the bearing is open: no shields or seals are fitted and lubrication is supplied by the application. For normal-load mounting with a rotating inner ring on a 55 mm shaft, typical catalogue practice is a k5 shaft seat with an H7 housing bore — verify against the actual load direction and magnitude. In the SKF catalogue this open execution carries the bare designation; protected variants are ordered separately as -2Z and -2RSH.
Typical equipment & failure modes
Common applications
- industrial fans
- industrial electric motors
- centrifugal and positive-displacement pumps
- gearboxes and speed reducers
Known failure patterns
- contamination wear from dust and dirt ingress through the open arrangement
- lubricant starvation when no regreasing interval is maintained
- raceway smearing under marginal lubrication at start-up
- edge loading from shaft deflection or housing misalignment
Selection pitfalls — read before you substitute
- At 55 mm bore, induction heating to roughly 80–100 °C is the clean mounting method; never exceed 120 °C, and hold 6311 against the shaft shoulder while it cools so the ring cannot creep back.
- The 63xx medium series gains rating at 55 mm bore through a 120 mm OD and 29 mm width; the heavier rolling elements also trade away some speed versus a 6211.
- Storage matters for open bearings: 6311 leaves the factory with rust preventive only, so clean it and apply the service grease at assembly even if the rings look oily from the wrapper.
- Open bearings tolerate the highest speeds in the 6300-series but need a defined regreasing interval; run-to-failure lubrication is the dominant cause of early failure in open 6311 units.
- Vibration during standstill brinells the raceways of a 55 mm bearing at ball spacing; if the machine sits idle next to running equipment, turn the shaft over periodically or isolate the arrangement.
- Do not quieten a noisy bearing by preloading it: the 6300-series is a deep-groove design, not angular-contact; axial preload raises temperature and shortens grease life.
- The open 6311 needs external sealing and application-supplied lubrication; in the SKF catalogue the protected variants are separate order numbers 6311-2Z (shields) and 6311-2RSH (contact seals), not suffix-free 6311.
- The 74.1/45 kN ratings here are SKF Explorer-class figures from catalogue PUB BU/P1 17000/1 EN (Oct 2018); SKF can revise internal geometry and ratings without changing the designation, so treat the catalogue version and date as part of the specification and re-verify for critical drives.
Frequently asked questions
What are the dimensions of a 6311 bearing?
A 6311 deep-groove ball bearing has a 55 mm bore, 120 mm outer diameter and 29 mm width (2.165 × 4.724 × 1.142 in), per ISO 15 boundary dimensions. It is an open bearing with no seals or shields.
How should 6311 be mounted?
Apply the mounting force to the ring being fitted: on a 55 mm shaft seat the press load must pass through the inner-ring face only. Induction heating of the inner ring (max 120 °C) is the clean method at this size. Never strike the outer ring, the cage or the seals.
What lubrication does 6311 need?
The open 6311 is lubricated by the application; a NLGI 2 lithium-soap grease filled to roughly 25–35% of the free volume is the common choice, with a defined relubrication interval.
How does the 6311 bore code work?
The last two digits of 6311 are bore code 11, giving 11 × 5 = 55 mm bore. The 120 mm outside diameter and 29 mm width follow the ISO 15 diameter series, not the bore code alone.
What is the SKF designation and catalogue data for 6311?
In the SKF Rolling Bearings catalogue this size is listed as 6311 — the open (unsealed) execution, 55×120×29 mm per ISO 15. Quoted values: C 74.1 kN, C0 45 kN, Pu 1.9 kN, limiting speed 8000 r/min, mass 1350 g. Brand suffixes (2Z, 2RSH, 2RSL) differ from the industry-neutral spelling 6311.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018) on 2026-09-25. Read our editorial & correction policy.