NU311 bearing: complete specifications & equivalents
The NU311 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 |
| Tolerance class | P0 |
| Cage | polymer (PA66 glass-fibre reinforced) |
| Basic dynamic load rating C | 156 kN |
| Basic static load rating C0 | 143 kN |
| Fatigue load limit Pu | 18.6 kN |
| Reference speed (thermal) | 6000 rpm |
| Limiting speed (mechanical) | 7000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1450 g |
| Manufacturer designation | NU 311 ECP |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 6.1 single-row cylindrical roller bearings |
| Last verified | 2026-09-26 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 6.1 single-row cylindrical roller bearings) · extracted 2026-09-26
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 6.1 single-row cylindrical roller bearings); 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 & NU300-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 NU300-series | 17 mm |
| Largest outer diameter in NU300-series | 620 mm |
| Width range across NU300-series | 14–109 mm |
| Bore position in NU300-series (smallest first) | 9 of 34 |
| Bore above smallest NU300-series size | 38 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| NU311-NTN | NTN | 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 | SKF | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | Identical envelope but a different bearing type — confirm load and speed suitability before substitution. |
| 6311-2RS | SKF | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | Identical envelope but a different bearing type — confirm load and speed suitability before substitution. |
| 6311-ZZ | SKF | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | Identical envelope but a different bearing type — confirm load and speed suitability before substitution. |
| N311-ECP | SKF | full Dimensions and internal design equivalent — standard interchange. | Same ISO 15 boundary envelope and equivalent catalogue ratings; SKF N 311 ECP is a different execution with its own cage/flange configuration. |
| NJ311-ECP | SKF | full Dimensions and internal design equivalent — standard interchange. | Same ISO 15 boundary envelope and equivalent catalogue ratings; SKF NJ 311 ECP is a different execution with its own cage/flange configuration. |
| NUP311-ECP | SKF | full Dimensions and internal design equivalent — standard interchange. | Same ISO 15 boundary envelope and equivalent catalogue ratings; SKF NUP 311 ECP is a different execution with its own cage/flange configuration. |
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 NU311 model number is decoded
NU311 is a single-row cylindrical roller bearing in the NU300 family: line-contact rollers between ground inner and outer raceways, separated by a glass-fibre reinforced polyamide (PA66) cage, listed by SKF in SKF catalogue PUB BU/P1 17000. Numbering ties the bearing to its envelope: NU311 means cylindrical-roller type NU, standard series 3, 55 mm bore — which is why the 120×29 mm outline swaps dimensionally with other ISO 15 bearings of the same code. The SKF catalogue adds the ECP suffix for the standard glass-fibre reinforced polyamide cage; ECJ (pressed steel) and ECM (machined brass) are alternative executions with different speed and temperature ratings. Catalogue mass 1450 g for the 55×120×29 mm open execution covers the polymer cage and standard roller complement; steel or brass cage variants differ slightly in mass and carry their own order numbers. For a 55 mm shaft the usual inner-ring seat is k5 with an H6 housing when the inner ring rotates; the outer ring slides axially to accommodate thermal expansion of the shaft.
Typical equipment & failure modes
Common applications
- paper-machine wet-section rolls
- rolling-mill auxiliary gear trains
- crane hoist and trolley wheel shafts
- industrial gearbox input/output shafts
Known failure patterns
- inner-ring raceway spalling from overload or contamination in the line-contact hertz zone
- outer-ring raceway fatigue after extended service at loads above the catalogue L10 rating
- cage pocket wear from roller skidding at insufficient radial load or during start-up before oil film build-up
- roller-end scoring from inadequate oil flow in the roller-raceway contact
- hard-particle indentation of the raceway in unfiltered oil systems
Selection pitfalls — read before you substitute
- On this 55 mm bore, thermal expansion of the shaft can preload the inner ring if the fit is too tight; calculate the residual interference at operating temperature and confirm the outer ring can still slide axially in the housing.
- The NU300 series at 55 mm bore (120×29 mm) is the standard-section cylindrical roller envelope; stepping to a wide-section 22/23 variant changes OD, width and heat generation — it is not a drop-in swap when the housing and speed are fixed.
- Never press the outer ring through the roller complement during fitting: force for a press fit goes through the ring faces only, or brinell marks on the 120 mm race release as noise within the first running hours.
- The 1450 g mass and 29 mm width mean abutment faces must be square to the axis within the bearing's own P0 tolerance; a tilted spacer tilts the outer ring and concentrates load on one roller row of NU311.
- The 156/143 kN ratings are SKF catalogue 17000 values for the ECP polymer-cage execution; SKF can revise internal geometry without changing the order number, so keep the catalogue version (PUB BU/P1 17000/1 EN, 2018) with the specification and re-verify for critical drives.
- SKF lists several executions of NU311 (ECP polymer cage, ECJ pressed steel, ECM machined brass); they are not interchangeable order numbers — quote the full NU 311 ECP designation when purchasing and match the execution to the speed and temperature requirements.
Frequently asked questions
What are the dimensions and catalogue data of NU311?
The NU 311 ECP is a single-row cylindrical roller bearing with 55 mm bore, 120 mm outer diameter and 29 mm width (2.165 × 4.724 × 1.142 in) per ISO 15. From SKF catalogue PUB BU/P1 17000: basic dynamic load rating C 156 kN, C0 143 kN, fatigue load limit Pu 18.6 kN, reference speed 6,000 r/min, limiting speed 7,000 r/min, mass about 1450 g. It is an open, separable bearing with a glass-fibre reinforced polyamide cage.
How does the NU311 bore code work?
The last two digits of NU311 are bore code 11, so 11 × 5 = 55 mm bore. The 120 mm OD and 29 mm width come from the ISO 15 dimension-series plan, shared with other cylindrical bearings of the same code.
What does the ECP suffix mean on NU311?
ECP stands for a glass-fibre reinforced polyamide cage (PA66), the SKF standard for this size. Alternative executions include ECJ (pressed steel cage) and ECM (machined brass cage), which have different speed and temperature ratings and are separate order numbers.
Can NU311 take axial load?
No — the NU design has no ribs on the outer ring and cannot support axial load in either direction. It is intended for pure radial load with axial location provided by adjacent components. If axial location is required, consider NJ (one-direction) or NUP (two-direction) variants, or pair the NU bearing with a thrust or angular-contact bearing.
How does NU311 compare with a ball bearing of the same bore?
A cylindrical roller bearing has line contact and much higher radial capacity than a ball bearing of the same bore, but it cannot take axial load in the NU design and is sensitive to misalignment (≈ 3–4 minutes of arc). Speed limits are generally lower than deep-groove ball bearings. A ball bearing cannot be dropped into a pure radial cylindrical-roller position without re-checking life and deflection, and vice versa.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 6.1 single-row cylindrical roller bearings on 2026-09-26. Read our editorial & correction policy.