NJ311-ECP bearing: complete specifications & equivalents
The NJ311-ECP 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 | 1500 g |
| Manufacturer designation | SKF NJ 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 & NJ300-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 NJ300-series | 17 mm |
| Largest outer diameter in NJ300-series | 500 mm |
| Width range across NJ300-series | 14–95 mm |
| Bore position in NJ300-series (smallest first) | 9 of 29 |
| Bore above smallest NJ300-series size | 38 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| N311-ECP | SKF | full Dimensions and internal design equivalent — standard interchange. | Same ISO 15 envelope 55×120×29 mm and equivalent catalogue ratings; the N execution differs in flange/retaining-ring configuration — boundary-dimension interchangeable, but axial-locating behaviour is not identical. |
| NUP311-ECP | SKF | full Dimensions and internal design equivalent — standard interchange. | Same ISO 15 envelope 55×120×29 mm and equivalent catalogue ratings; the NUP execution differs in flange/retaining-ring configuration — boundary-dimension interchangeable, but axial-locating behaviour is not identical. |
| NU311 | SKF | full Dimensions and internal design equivalent — standard interchange. | Same ISO 15 envelope 55×120×29 mm and equivalent catalogue ratings; the NU execution differs in flange/retaining-ring configuration — boundary-dimension interchangeable, but axial-locating behaviour is not identical. |
| NU311 | SKF | full Dimensions and internal design equivalent — standard interchange. | Same ISO 15 envelope 55×120×29 mm and equivalent catalogue ratings; the NU execution differs in flange/retaining-ring configuration — boundary-dimension interchangeable, but axial-locating behaviour is not identical. |
| NU311 | SKF | full Dimensions and internal design equivalent — standard interchange. | Same ISO 15 envelope 55×120×29 mm and equivalent catalogue ratings; the NU execution differs in flange/retaining-ring configuration — boundary-dimension interchangeable, but axial-locating behaviour is not identical. |
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 NJ311-ECP model number is decoded
NJ311-ECP is the 55 mm bore entry in the NJ300 range: a 55×120×29 mm single-row caged cylindrical roller bearing with a glass-fibre reinforced polyamide (PA66) window-type cage, rated C 156 kN / C0 143 kN. Reading the NJ prefix: two integral flanges on the inner ring and no flanges on the outer ring; the inner ring retains the roller set. This makes the execution able to locate the shaft axially in one direction; an HJ angle ring on the opposite side converts it into two-direction location. Reading the order-string suffix ECP: the E-design execution with a glass-fibre reinforced polyamide (PA66) cage, limited to 120 °C continuous. Selection arithmetic: C0/C ≈ 0.92 (143 against 156 kN), and the Pu figure 18.6 kN is the fatigue load-limit floor for the SKF life equation; the catalogue lists 6,000 r/min thermal reference speed and 7,000 r/min mechanical limiting speed. Fit practice for NJ311-ECP: orient the inner-ring flange side toward the axial load direction; if an HJ angle ring is used, verify its fit and clearance before locking the arrangement. Single-row cylindrical rollers tolerate only about 3–4 minutes of arc misalignment, so verify shaft and housing alignment.
Typical equipment & failure modes
Common applications
- medium industrial gearbox shafts
- electric-motor shafts in pumps and fans
- compressor crank and rotor shafts
- machine-tool radial spindle supports
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
- polymer cage softening above 120 °C
- polymer cage cracking or softening after sustained running above 120 °C or with incompatible lubricant
- roller-end scoring from inadequate oil flow in the roller-raceway contact
- edge-loading fatigue after shaft deflection beyond the 3–4 minute alignment limit
- fretting corrosion on a loose rotating shaft seat or in a vibratory stand-still
Selection pitfalls — read before you substitute
- Do not use a NJ bearing where two-direction axial location is required without an HJ angle ring
- The dimension series 3 (medium-section ISO 15 envelope) envelope is shared with the N/NU/NJ/NUP executions of 311, but flange configuration and axial-locating behaviour differ — quote the full SKF NJ 311 ECP and do not substitute rib styles without checking the shaft locating scheme.
- Shaft and housing fillets must clear the bearing chamfers; an oversized radius tilts the 29 mm-wide ring and concentrates load.
- Press-fit force goes through ring faces only; driving a ring home through the rollers brinells the 120 mm raceway.
- The 156/143 kN ratings are SKF catalogue 17000 (2018) values for the ECP execution; re-verify against the current catalogue for critical drives and keep the catalogue version with the specification.
Frequently asked questions
What are the dimensions and catalogue data of NJ311-ECP?
SKF NJ 311 ECP is a single-row caged cylindrical roller bearing with 55 mm bore, 120 mm OD and 29 mm width per ISO 15. SKF lists C 156 kN, C0 143 kN, Pu 18.6 kN, reference speed 6,000 r/min and limiting speed 7,000 r/min, mass about 1500 g.
What does the NJ designation and ECP suffix mean?
The ECP suffix marks the E-design execution with a glass-fibre reinforced polyamide (PA66) cage, limited to 120 °C continuous. Structurally this execution has two integral flanges on the inner ring and no flanges on the outer ring; the inner ring retains the roller set.
Can NJ311-ECP take axial load and locate the shaft?
In one direction only, via the two inner-ring flanges. Add an HJ angle ring on the opposite side for two-direction location.
How does NJ311-ECP compare with the other executions in the same envelope?
The N/NU/NJ/NUP executions share the ISO 15 envelope and load ratings but differ in flange arrangement and axial-locating behaviour; quote the exact order number.
What limits the service life of this bearing most often?
Line-contact fatigue above the L10 rating, cage wear at light loads and high temperatures, and edge loading from misalignment beyond about 3–4 minutes of arc are the typical failure drivers.
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.