21318 bearing: complete specifications & equivalents
The 21318 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 | 6100 g |
| Manufacturer designation | SKF 21318 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 | 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. |
| 6318 | 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. |
| 6318-2RS | 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. |
| 6318-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. |
| 21318-EK | SKF | full Dimensions and internal design equivalent — standard interchange. | Tapered-bore (1:12) execution on H318 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 21318 model number is decoded
21318 E belongs to the SKF spherical roller range — the 90 mm bore entry in the 21300-series series (dimension series 13 (heavy OD, normal width)), dimensioned 190 mm OD and 43 mm wide. The code breaks down as type digit 2 (double-row spherical roller), dimension series 13 (dimension series 13 (heavy OD, normal width)), and bore code 18 = 90 mm; dimensions 90×190×43 mm therefore match the ISO 15 envelope. 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 6100 g for the 90×190×43 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 21318 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
- marine propulsion and thruster shafts
- cement-mill trunnion and drive shafts
- heavy conveyor head shafts in mining
- jaw and cone crusher 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
- stamped-steel cage fatigue after long service in high-vibration screening duty without the VA405 execution
- surface distress and smearing when the relubrication interval is exceeded — the W33 groove is only effective if grease actually reaches the roller rows
- rolling-contact fatigue spalling after the rated L10 life is exceeded
Selection pitfalls — read before you substitute
- Mount the 90 mm bore 21318 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 6100 g mass and 43 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 21318.
- 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 393/450 kN ratings are SKF catalogue values for this exact execution (21318 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 21318 (cylindrical bore as listed, tapered-bore 21318 EK variant, plus sealed and vibrating-screen options in the same envelope); they are not interchangeable order numbers — quote the full 21318 E designation when purchasing.
Frequently asked questions
What are the dimensions and catalogue data of 21318?
The 21318 E is a double-row spherical roller bearing with 90 mm 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: basic dynamic load rating C 393 kN, C0 450 kN, fatigue load limit Pu 45.5 kN, reference speed 3,600 r/min, limiting speed 4,800 r/min, mass about 6100 g. It is an open, self-aligning bearing with a stamped window-type steel cage.
How does the 21318 bore code work?
The last two digits of 21318 are bore code 18, so 18 × 5 = 90 mm bore. The 190 mm OD and 43 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 21318?
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 21318 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 21318K 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 21318 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.