21318K bearing: complete specifications & equivalents
The 21318K 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 | 6210 g |
| Manufacturer designation | NTN 21318K |
| 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 | — |
| 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 NTN 21300-series envelope, cage and ratings; this is the tapered-bore execution (K, 1:12) of the cylindrical-bore 21318-NTN — mounting (adapter/withdrawal sleeve or tapered seat, drive-up) differs. Verify shaft arrangement. |
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 21318K model number is decoded
21318K is the C design-code execution of NTN's spherical roller range for a 90 mm shaft — 355 kN basic dynamic capacity in a 6210 g, open ISO 15 envelope. Numbering ties 21318K to its envelope and execution: same-number EA versus EM or plain variants share the 90 mm bore but differ in cage and sometimes mass, so they are quoted as separate articles. The 50.0 mm radial section over the 90 mm bore carries two roller rows; capacity per millimetre of bore is about 3.9 kN/mm, among the highest of rolling bearings for the ISO 15 envelope. Equivalent-load planning keeps a radial plus moderate axial combination on 21318K; if the axial component dominates, pair with a thrust bearing rather than running one roller row unloaded. After mounting on a tapered seat, lock the nut and re-check clearance after a short running-in period, because sleeve seating and ring lift-off can change the residual clearance of the 90 mm set.
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
- raceway spalling at the roller ends when misalignment or deflection concentrates the line contact
- machined EM cage wear from inadequate oil film at the cage-guiding surfaces
- sliding wear and heat when relubrication intervals ignore the groove (D1/W33) supply path
- hard-particle indentation through the open arrangement in dusty mining duty
- asymmetric wear on the two roller rows from sustained angular misalignment beyond the self-aligning range
Selection pitfalls — read before you substitute
- Mount the 90 mm ring with induction heat or the sleeve drive-up procedure; at 6210 g cocking damages the spherical raceways, and repositioning after seating is impractical.
- Self-aligning does not mean unlimited misalignment: beyond the catalogue angle the outer ring's spherical travel is exhausted and the 355 kN rating no longer applies.
- The D1/W33 groove only helps if the housing has a matching grease passage; mounting a grooved 21318K in a solid block with no port wastes the feature and leaves the centre rows under-lubricated.
- The D1/W33 groove only helps if the housing has a matching grease passage; mounting a grooved 21318K in a solid block with no port wastes the feature and leaves the centre rows under-lubricated.
- 213-series C/CK executions use the C cage/design code — CK adds the 1:12 tapered bore; quote 21318K in full because a C cannot be mounted on an adapter-sleeve tapered seat.
- The 355/400 kN ratings, 50.5 kN Pu and 6210 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for 21318K (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 21318K?
21318K 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 6210 g. It is open, with pressed-steel cage of the 213-series C design and a 1:12 tapered bore.
What is the difference between the K/K30 tapered bore and the cylindrical bore versions?
K denotes a 1:12 tapered bore. 21318K mounts on an adapter sleeve (or tapered shaft seat) and is driven up to the specified residual clearance; its cylindrical-bore counterpart in the same envelope and ratings is 21318.
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. 21318K is the C design-code execution.
What do D1 and W33 mean on 21318K?
21318K 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 21318K 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.