21318-NTN bearing: complete specifications & equivalents
The 21318-NTN 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 | NTN |
| 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 | 355 kN |
| Basic static load rating C0 | 400 kN |
| Fatigue load limit Pu | 50.5 kN |
| Limiting speed (mechanical) | 2300 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 6300 g |
| Manufacturer designation | NTN 21318 |
| Standard | ISO 15 |
| Catalog version | NTN Ball and Roller Bearings CAT.No.2203E |
| Last verified | 2026-10-01 |
Source: catalog reference (NTN Ball and Roller Bearings CAT.No.2203E) · extracted 2026-10-01
Parameters extracted from the official NTN Ball and Roller Bearings catalogue (NTN Ball and Roller Bearings CAT.No.2203E); NTN® is a trademark of NTN Corporation, used here for identification only — mpnbase is not an authorized NTN distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at ntnglobal.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 |
|---|---|---|---|
| 21318K | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same NTN 21300-series envelope, cage and ratings; this is the cylindrical-bore execution of the tapered-bore 21318K (K/K30 sleeve or tapered-seat mounting). Verify shaft arrangement. |
| 21318 | SKF | 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-EK | SKF | 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. |
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-NTN model number is decoded
The NTN order number 21318 identifies a 90×190×43 mm (3.543 × 7.48 × 1.693 in) spherical roller bearing, cylindrical bore, to the ISO 15 boundary plan. Reading the full code: the number gives the 90×190 mm envelope, C/CK names the cage/capacity execution, no bore suffix means cylindrical bore for a direct shaft seat, and plain outer ring (no D1/W33 groove) completes the order number. Two symmetric roller rows share the load: C 355 kN, C0 400 kN (C0/C ≈ 1.13), with useful axial capacity in either direction alongside the dominant radial load. Catalogue mass 6300 g (6.30 kg) for the 90×190×43 mm execution includes the C design-code cage and both roller rows; shaft and housing shoulders must support that ring squarely. Fit the cylindrical-bore 21318 with the inner ring heated (max 120 °C) for the shaft interference; the outer ring slides into the housing with its spherical seat able to pivot after seating.
Typical equipment & failure modes
Common applications
- wind-turbine gearbox and rotor bearings
- large vibrating screens and mining feeders
- heavy conveyor and bucket-excavator pulleys
- jaw/cone crusher eccentric and shaft positions
Known failure patterns
- lubricant starvation at the centre rib area when the D1/W33 groove is not connected to a relubrication supply
- machined EM cage wear from inadequate oil film at the cage-guiding surfaces
- micro-pitting when the EHL film is thinner than the raceway composite roughness
- brinelling from static overload or a hammer blow during sleeve mounting
- hard-particle indentation through the open arrangement in dusty mining duty
Selection pitfalls — read before you substitute
- Mount the 90 mm ring with induction heat or the sleeve drive-up procedure; at 6300 g cocking damages the spherical raceways, and repositioning after seating is impractical.
- Minimum load must be maintained even at rest under vibration: an unloaded 21318 on a stopped screen false-brinells; parking brakes and shaker isolation both matter.
- Never substitute 21318 by envelope alone: the 400 kN C0 and 50.5 kN Pu are specific to the NTN C design-code execution, and vibrating duty depends heavily on cage identity.
- Open spherical rollers swallow dust in mining duty; specify labyrinth or taconite seals externally, or the 2,300 r/min grease rating is lost to abrasive wear long before fatigue.
- Adapter-sleeve mounting requires the correct sleeve series and locknut for the 90 mm shaft; a sleeve sized to bore alone ignores thread, width and the oil-injection option on large K seats.
- The 355/400 kN ratings, 50.5 kN Pu and 6300 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for 21318 (C design-code); another maker's same-envelope part revises internal geometry, so re-verify ratings and cage before substitution on vibrating or rated drives.
Frequently asked questions
What are the dimensions and catalogue data of 21318?
21318 is an NTN double-row spherical roller bearing to ISO 15: 90 mm bore, 190 mm OD and 43 mm width (3.543 × 7.48 × 1.693 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 355 kN, C0 400 kN, Pu 50.5 kN, grease limiting speed 2,300 r/min, oil 3,000 r/min, mass about 6300 g. It is open, with pressed-steel cage of the 213-series C design.
What is the difference between the K/K30 tapered bore and the cylindrical bore versions?
21318 has a cylindrical bore and mounts directly on a machined shaft seat. Its tapered-bore counterpart is 21318K (K = 1:12, or K30 = 1:30 on the wide series), intended for adapter/withdrawal-sleeve mounting.
What do EA and EM mean on NTN spherical roller bearings?
EA is the NTN standard-capacity/high-capacity execution with a pressed sheet-steel window cage; EM is the high-capacity execution with a one-piece machined brass cage. Both use the optimised symmetric-roller design, but cage identity changes mass, speed behaviour and suitability for duties like vibrating screens, so they are separate order numbers. 21318 is the C design-code execution.
What do D1 and W33 mean on 21318?
21318 is listed without a D1/W33 outer-ring groove in 2203E; lubrication is supplied from the ring sides. D1 (NTN spelling) and W33 add the annular groove plus holes and are ordered as distinct suffixed executions of the same envelope.
How much misalignment and axial load can 21318 take?
The sphered outer raceway compensates static and dynamic misalignment in the order of 1–2° (verify the exact 2203E figure for the 21300 series); beyond that, load concentrates on one roller row. Load is predominantly radial with a moderate axial share in either direction — 355 kN C / 400 kN C0 — but sustained pure axial load is not recommended because it unloads one row.
Reviewed & verified by the MPN Base engineering desk against source catalog NTN Ball and Roller Bearings CAT.No.2203E on 2026-10-01. Read our editorial & correction policy.