21311 bearing: complete specifications & equivalents
The 21311 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 | steel |
| Basic dynamic load rating C | 159 kN |
| Basic static load rating C0 | 166 kN |
| Fatigue load limit Pu | 18.6 kN |
| Reference speed (thermal) | 5600 rpm |
| Limiting speed (mechanical) | 7500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1700 g |
| Manufacturer designation | SKF 21311 E |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 9.1 spherical roller bearings |
| Last verified | 2026-09-26 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 9.1 spherical 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. 9.1 spherical 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 & 21300-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 21300-series | 40 mm |
| Largest outer diameter in 21300-series | 240 mm |
| Width range across 21300-series | 23–50 mm |
| Bore position in 21300-series (smallest first) | 4 of 14 |
| Bore above smallest 21300-series size | 15 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 21311-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 | 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. |
| 21311-EK | SKF | full Dimensions and internal design equivalent — standard interchange. | Tapered-bore (1:12) execution on H311 adapter sleeve; same ISO 15 envelope, separate order number. |
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 21311 model number is decoded
21311 E belongs to the SKF spherical roller range — the 55 mm bore entry in the 21300-series series (dimension series 13 (heavy OD, normal width)), dimensioned 120 mm OD and 29 mm wide. Numbering ties the bearing to its envelope: 21311 means spherical-roller type, dimension series 13, 55 mm bore — which is why the 120×29 mm outline swaps dimensionally with other ISO 15 bearings of the same code. The trailing E is the SKF optimized internal design: larger rollers and a stamped window-type steel cage give higher load ratings than the older CC geometry; EK is the same bearing with a 1:12 tapered bore for adapter sleeves. Catalogue mass 1700 g for the 55×120×29 mm open execution covers the a stamped window-type steel cage; tapered-bore and sealed variants differ in mass and carry their own order numbers. After mounting, swing the outer ring to confirm free self-alignment: the 21311 should tilt through its full catalogue misalignment range without binding; a stiff joint signals a cocked seat or shoulder interference.
Typical equipment & failure modes
Common applications
- hammer-mill and crusher rotors
- continuous-caster guide rolls
- extruder gearbox shafts
- vibrating screen and scalper main shafts
Known failure patterns
- raceway fatigue spalling of the sphered outer raceway after extended service above the catalogue L10 rating
- inner-ring raceway spalling from edge loading when misalignment exceeds the self-aligning recovery range
- cage pocket wear or fracture from roller skew at insufficient minimum load or rapid acceleration
- roller-end scoring from starved lubricant at start-up before the grease channel purges
- fretting corrosion on a loose rotating shaft seat or in vibratory stand-still
Selection pitfalls — read before you substitute
- On this 55 mm bore, an interference inner-ring fit consumes a large share of the CN clearance; specify C3 when the inner ring rotates hot, and verify residual clearance after mounting rather than trusting the catalogue clearance class.
- The 21300-series series at 55 mm bore (120×29 mm) pairs a heavy OD with a narrow section — a compact way to add capacity, but the shoulder and abutment diameters differ from the 222 series; it is not a drop-in swap.
- The 1700 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 21311.
- The self-aligning feature is not a license to ignore alignment: beyond ≈ 0.5–2.5° (series-dependent) the edge loading eats the fatigue margin, and seal drag grows as the rings tilt.
- The 159/166 kN ratings are SKF catalogue values for this exact execution (21311 E); SKF can revise internal geometry without changing the order number, so keep the catalogue version (SKF catalogue PUB BU/P1 17000) with the specification and re-verify for critical drives.
- SKF lists several executions of 21311 (cylindrical bore as listed, tapered-bore 21311 EK variant, plus sealed and vibrating-screen options in the same envelope); they are not interchangeable order numbers — quote the full 21311 E designation when purchasing.
Frequently asked questions
What are the dimensions and catalogue data of 21311?
The 21311 E is a double-row spherical 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 159 kN, C0 166 kN, fatigue load limit Pu 18.6 kN, reference speed 5,600 r/min, limiting speed 7,500 r/min, mass about 1700 g. It is an open, self-aligning bearing with a stamped window-type steel cage.
How does the 21311 bore code work?
The last two digits of 21311 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 (dimension series 13 (heavy OD, normal width)), shared with other spherical roller bearings of the same code.
What does the E suffix mean on 21311?
E is the SKF optimized internal design with larger rollers and a stamped window-type steel cage for higher load ratings. The EK variant is the same bearing with a 1:12 tapered bore for adapter sleeves.
Can 21311 accommodate misalignment and axial load?
Yes on both counts. The sphered outer raceway lets the bearing self-align ≈ 0.5–2.5° depending on series, absorbing shaft deflection and housing-seat errors. The two barrel-roller rows also carry bidirectional axial load in addition to heavy radial load — this is the key difference from cylindrical roller bearings, which take no axial load.
When should the tapered-bore 21311K variant be used instead?
Choose the K (1:12 tapered bore) variant when the bearing must seat on an adapter or withdrawal sleeve — typical for long shafts, frequent dismounting, or stepped shafts where machining a precision journal is impractical. Sleeve mounting requires measuring clearance reduction or axial drive-up, not nut torque. The cylindrical-bore 21311 listed here seats directly on a machined journal.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 9.1 spherical roller bearings on 2026-09-26. Read our editorial & correction policy.