21311-EK bearing: complete specifications & equivalents
The 21311-EK 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 | 1950 g |
| Manufacturer designation | SKF 21311 EK |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 9.2 adapter-sleeve executions |
| Last verified | 2026-09-26 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 9.2 adapter-sleeve executions) · extracted 2026-09-26
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 9.2 adapter-sleeve executions); 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. |
| 21311 | SKF | full Dimensions and internal design equivalent — standard interchange. | Tapered-bore (1:12) sleeve-mounted execution of 21311; identical ISO 15 envelope, fits H311 adapter sleeve on a 50 mm shaft. |
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-EK model number is decoded
In SKF catalogue PUB BU/P1 17000, 21311-ek denotes the tapered-bore version (K suffix, taper 1:12) of the 21300-series spherical roller bearing: dimensioned 55×120×29 mm, it seats on an adapter or withdrawal sleeve rather than directly on a machined journal. Reading the designation: the leading 2 marks a spherical roller bearing, the 13 is the ISO 15 dimension series (dimension series 13 (heavy OD, normal width)), and the last two digits encode the 55 mm bore; the 120 mm OD and 29 mm width follow the ISO 15 general plan. Note that K means 1:12 taper; the rarer K30 suffix means 1:30. Adapter sleeves (H) and withdrawal sleeves (AH) are ordered separately by shaft diameter, and the KM locknut plus MB lock washer used for drive-up are also separate components. Selection arithmetic: the C0/C ratio is about 1.04 (static 166 kN against dynamic 159 kN), typical of a spherical roller sized for heavy combined loads, and the 18.6 kN fatigue load limit Pu is the equivalent-load floor used in the life calculation. Over-driving the 21311-ek up its sleeve pinches radial clearance below the residual minimum and can crack the inner ring in service; under-driving leaves the sleeve seat loose, so the ring creeps and frets the sleeve — measure, do not estimate.
Typical equipment & failure modes
Common applications
- vibrating screen and scalper main shafts
- conveyor drive and bend pulleys
- shafting produced to commercial tolerances, where the adapter sleeve supplies the precision seat
- split-housing plummer block arrangements with bearings swapped in situ
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
- sleeve seizure and shaft seat damage from omitting the anti-seize film between withdrawal sleeve and journal before drive-up
- roller-end scoring from starved lubricant at start-up before the grease channel purges
- electrical pitting on VFD-driven shafts without grounding protection
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.
- A loose sleeve after the first weeks of service usually means inadequate initial drive-up; re-checking clearance without dismounting is possible through the 29 mm-wide roller rows with feeler gauges — do not simply tighten the KM nut until vibration stops.
- A loose sleeve after the first weeks of service usually means inadequate initial drive-up; re-checking clearance without dismounting is possible through the 29 mm-wide roller rows with feeler gauges — do not simply tighten the KM nut until vibration stops.
- Never use the tapered-bore EK/K variant's drive-up figures on this cylindrical-bore 21311-ek; clearance reduction targets differ, and over-driving a cylindrical bore onto an oversized journal cracks the inner ring.
- The 159/166 kN ratings are SKF catalogue values for this tapered-bore execution (SKF 21311 EK); sleeve, KM nut and MB washer are separate order numbers, and the catalogue version (SKF catalogue PUB BU/P1 17000) should travel with the mounting specification.
Frequently asked questions
What are the dimensions and catalogue data of 21311-ek?
The SKF 21311 EK is a double-row spherical roller bearing with a 1:12 tapered bore, 55 mm nominal 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: C 159 kN, C0 166 kN, Pu 18.6 kN, reference speed 5,600 r/min, limiting speed 7,500 r/min, mass about 1950 g. It is mounted on an adapter (H) or withdrawal (AH) sleeve, not directly on the shaft.
What does the K suffix mean on 21311-ek?
K marks a 1:12 tapered bore for sleeve mounting — SKF writes EK or CCK(/W33), FAG writes -K- inside the suffix chain for sleeve mounting. The bearing seats on an H-series adapter sleeve with a KM locknut and MB lock washer (plain shaft, h9 tolerance), or on an AH withdrawal sleeve against a shaft shoulder. The rarer K30 suffix would instead mean a 1:30 taper; dimension series 40/41 spherical rollers commonly use it.
Which adapter sleeve fits the 21311-ek?
The sleeve is selected by the actual shaft diameter in millimetres, not only by the 55 mm nominal bore: SKF H-sleeve numbers each cover a small shaft-diameter range and are width-series specific (H39/H30/H31/H32 matching dimension series 39/40/31/32), and each kit bundles the sleeve, KM locknut and MB lock washer. For shoulder locations use an AH withdrawal sleeve instead. Confirm the sleeve number against the SKF catalogue PUB BU/P1 17000 mounting tables for your shaft size.
How is the 21311-ek driven up and checked?
Mounting is controlled by radial-clearance reduction or axial drive-up distance from the SKF catalogue tables for the 1:12 taper, never by locknut torque. Measure clearance with feeler gauges before and after tightening the KM nut, stop at the tabulated decrease, and lock the MB washer tab. Over-drive removes too much clearance (inner-ring cracking risk); under-drive lets the sleeve creep and fret.
What is the difference between 21311-ek and 21311?
They share the ISO 15 envelope and the same 159/166 kN ratings, but 21311-ek has the 1:12 tapered bore for sleeve mounting on a plain shaft, while 21311 has a cylindrical bore for direct mounting on a machined interference journal (typically k5 with H7 housing). They are separate order numbers, not interchangeable in the same shaft arrangement.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 9.2 adapter-sleeve executions on 2026-09-26. Read our editorial & correction policy.