6311-ZZ bearing: complete specifications & equivalents
The 6311-ZZ is a ISO 15 radial bearing sized 55 x 120 x 29 mm (bore x OD x width) with ZZ sealing. 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 | ZZ |
| 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) | 6300 rpm |
| Operating temperature | -30 to +120 °C |
| Mass | 1400 g |
| Manufacturer designation | SKF 6311-2Z |
| 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 (ZZ 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; seal variant (ZZ vs OPEN) and load ratings differ — confirm sealing and rating 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; catalogue load ratings differ by >10% — re-rate the application before substituting. |
| 6311 | ISO 15 | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | ISO 15 boundary-dimension envelope; seal suffix convention varies by brand (2RS / DDU / LLU / 2RSR) — verify seal design and temperature range before substituting. |
| 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 (ZZ vs 2RS) — confirm sealing suits the duty. |
| 6311-NSK | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 55×120×29 mm envelope per ISO 15; seal variant differs (ZZ vs OPEN) — confirm sealing suits the duty. |
| 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 (ZZ vs RSR) — confirm sealing suits the duty. |
| 6311-ZZ-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. |
| 6311-2RS-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 55×120×29 mm envelope per ISO 15; seal variant differs (ZZ vs 2RS) — confirm sealing suits the duty. |
| 6311-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 55×120×29 mm envelope per ISO 15; seal variant differs (ZZ vs OPEN) — confirm sealing suits the duty. |
| 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 (ZZ vs RSR) — confirm sealing suits the duty. |
| 6311-ZZ-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. |
| 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-ZZ model number is decoded
6311-ZZ carries two non-contact sheet-steel shields that hold the factory grease in and keep coarse debris out; they do not seal against liquids. Within the medium 63xx section (diameter series 3 of ISO 15), multiplying bore code 11 by five gives the 55 mm bore; the 120 mm outside diameter and 29 mm width follow the same boundary-dimension plan. For a rotating inner ring on a 55 mm shaft under normal load, catalogue practice seats it on a k5 shaft fit with an H7 housing bore — confirm against the actual load direction and magnitude before committing. SKF's own suffix is 2Z (this page's industry-neutral spelling is -ZZ); catalogue number 6311-2Z.
Typical equipment & failure modes
Common applications
- industrial fans
- industrial electric motors
- centrifugal and positive-displacement pumps
- gearboxes and speed reducers
Known failure patterns
- fine-particle abrasion when non-contact shields let dust past in dirty duty
- grease aging in the shield-for-life cavity with no relubrication path
- false brinelling from vibration while the shaft is stationary
- fretting corrosion on a loose shaft seat
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 section at 55 mm bore gains dynamic rating through larger rolling elements on a 120 mm OD; the penalty is mass and a lower limiting speed than the 6211 — do not specify it for speed-critical shafts.
- Do not wash 6311-ZZ in solvent before mounting: the grease inside the shielded cavity is the service fill, and solvent creeping past the shield gap strips it out.
- Shielded 6311-ZZ units are typically greased for life; prying the shields out for regreasing usually bends them and leaves a gap that throws grease in service.
- Never mix components between two 6311-ZZ units: rings, cage and balls are factory-matched and are not field-interchangeable, even between identical designations.
- A 55 mm bore listing showing the right d/D/B but no standard or precision-class reference may be a loose-tolerance import; measure bore/OD spread before fitting it to a machined shaft.
- SKF spells the shielded version 6311-2Z (one shield: 6311-Z), not "-ZZ": the suffix language differs by brand even though the ISO envelope is identical, so quote the brand designation when ordering.
- The single-shield execution 6311-Z is a distinct order number in catalogue 17000: it suits open gears or oil-bath arrangements where the unshielded face faces the lubricant, and it is not interchangeable with the double-shield 6311-2Z for high-contamination positions.
- 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-ZZ bearing?
A 6311-ZZ 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 fitted with two non-contact metallic shields.
How does the 6300 compare with other series at the same 55 mm bore?
The '3' is the medium diameter series: 120×29 mm, 32.5 mm radial section at 55 mm bore, carrying more load than a 6211 but needing a larger housing bore and giving up some speed.
Are 6311 bearings from different brands interchangeable?
For boundary dimensions, yes: every brand's 6311 uses the same ISO 15 envelope (55×120×29 mm). Load ratings, limiting speeds, clearance, precision class and sealing design can differ, so verify those in the supplier catalogue when substituting. Seal suffixes also differ by brand (2RS, DDU, LLU, 2RSL and similar).
What internal clearance does 6311-ZZ have?
Unless a clearance suffix says otherwise, 6311-ZZ is manufactured to normal (CN) radial internal clearance. Tight fits and hot shafts consume clearance in service — for those conditions order the C3 execution of 6311 and verify the residual clearance after mounting.
What is the SKF designation and catalogue data for 6311-ZZ?
In the SKF Rolling Bearings catalogue this size is listed as 6311-2Z — two non-contact sheet-metal shields, 55×120×29 mm per ISO 15. Quoted values: C 74.1 kN, C0 45 kN, Pu 1.9 kN, limiting speed 6300 r/min, mass 1400 g. Brand suffixes (2Z, 2RSH, 2RSL) differ from the industry-neutral spelling 6311-ZZ.
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.