21318-EK bearing: complete specifications & equivalents
The 21318-EK is a ISO 15 radial bearing sized 90 x 190 x 43 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 90 mm |
| Outer diameter D | 190 mm |
| Width B | 43 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 393 kN |
| Basic static load rating C0 | 450 kN |
| Fatigue load limit Pu | 45.5 kN |
| Reference speed (thermal) | 3600 rpm |
| Limiting speed (mechanical) | 4800 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 7250 g |
| Manufacturer designation | SKF 21318 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 | 3.543 in |
|---|---|
| Outer diameter D | 7.48 in |
| Width B | 1.693 in |
| ISO bore code | 18 |
| Radial section height (D−d)/2 | 50 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) | 11 of 14 |
| Bore above smallest 21300-series size | 50 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 21318-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 90×190×43 mm envelope per ISO 15; catalogue load ratings differ by >10% — re-rate the application before substituting. |
| 21318 | SKF | full Dimensions and internal design equivalent — standard interchange. | Tapered-bore (1:12) sleeve-mounted execution of 21318; identical ISO 15 envelope, fits H318 adapter sleeve on a 80 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 21318-EK model number is decoded
21318-ek is the 1:12 tapered-bore execution of the 21300-series spherical roller bearing: the same two barrel-roller rows on a sphered outer raceway as 21318, but the inner-ring bore tapers 1 mm per 12 mm for adapter- or withdrawal-sleeve mounting, as listed by SKF in SKF catalogue PUB BU/P1 17000. Digit by digit, 21318-ek reads as bearing type 2 (spherical roller, two barrel-roller rows), dimension series 13, and bore reference 18 resolving to 90 mm; 190 mm OD and 43 mm width are the matching ISO 15 boundary values. 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. The 50.0 mm radial section height ((190−90)/2) and 7250 g catalogue mass frame a 90 mm bore bearing rated at 393 kN C — roughly 4.37 kN of dynamic capacity per millimetre of bore before application factors. At 90 mm bore, dismount after service is by KM locknut reversal or a hydraulic nut on larger sizes; oil-injection grooves on the bigger sleeves let pressurised oil float the 21318-ek off the taper without scoring either surface.
Typical equipment & failure modes
Common applications
- rolling-mill pinion and back-up shafts
- large vibrating screens and feeders
- heavy crusher and screen shafts mounted and dismounted with hydraulic nuts
- long through-shafts in conveyors, where a sleeve seat avoids a precision journal
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
- seal-lip wear and grease purge loss when an open bearing is run without functioning housing seals
Selection pitfalls — read before you substitute
- Mount the 90 mm bore 21318-ek by induction heating (max 120 °C) or oil injection — driving a bearing of this section home through the rollers brinells both raceways, and the damage only speaks up as vibration hours later.
- The 21300-series series at 90 mm bore (190×43 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 21318-ek and its cylindrical-bore counterpart 21318 share envelope and load ratings (393/450 kN) but are not interchangeable in a housing already fitted for direct shaft mounting — the sleeve changes the assembly stack-up.
- A loose sleeve after the first weeks of service usually means inadequate initial drive-up; re-checking clearance without dismounting is possible through the 43 mm-wide roller rows with feeler gauges — do not simply tighten the KM nut until vibration stops.
- Open spherical roller bearings rely on the housing seals; in screening or crusher duty a failed seal lets grit into the sphered raceway and the 21318-ek pits long before its L10 life.
- The 393/450 kN ratings are SKF catalogue values for this tapered-bore execution (SKF 21318 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 21318-ek?
The SKF 21318 EK is a double-row spherical roller bearing with a 1:12 tapered bore, 90 mm nominal bore, 190 mm outer diameter and 43 mm width (3.543 × 7.48 × 1.693 in) per ISO 15. From SKF catalogue PUB BU/P1 17000: C 393 kN, C0 450 kN, Pu 45.5 kN, reference speed 3,600 r/min, limiting speed 4,800 r/min, mass about 7250 g. It is mounted on an adapter (H) or withdrawal (AH) sleeve, not directly on the shaft.
What does the K suffix mean on 21318-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 21318-ek?
The sleeve is selected by the actual shaft diameter in millimetres, not only by the 90 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 21318-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 21318-ek and 21318?
They share the ISO 15 envelope and the same 393/450 kN ratings, but 21318-ek has the 1:12 tapered bore for sleeve mounting on a plain shaft, while 21318 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.