21311K bearing: complete specifications & equivalents
The 21311K 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 | NTN |
| 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 | 161 kN |
| Basic static load rating C0 | 163 kN |
| Fatigue load limit Pu | 16.1 kN |
| Limiting speed (mechanical) | 3700 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1690 g |
| Manufacturer designation | NTN 21311K |
| 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 | 2.165 in |
|---|---|
| Outer diameter D | 4.724 in |
| Width B | 1.142 in |
| ISO bore code | — |
| 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 | 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 21311-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 21311K model number is decoded
21311K is the C design-code execution of NTN's spherical roller range for a 55 mm shaft — 161 kN basic dynamic capacity in a 1690 g, open ISO 15 envelope. Reading the full code: the number gives the 55×120 mm envelope, C/CK names the cage/capacity execution, K marks the 1:12 tapered bore for adapter/withdrawal-sleeve mounting, and plain outer ring (no D1/W33 groove) completes the order number. The 1:12 tapered bore mounts on an adapter/withdrawal sleeve (or tapered seat); drive-up sets the residual radial clearance and fixes the axial position of the 55 mm bore assembly. Selection: the C0/C ratio of 1.01 (163/161 kN) reflects the heavy static and shock proportioning of 21311K; size the equivalent load at the required L10 with shock factor for the application. 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 55 mm set.
Typical equipment & failure modes
Common applications
- marine propulsion auxiliary shafts
- vibrating screen and feeder shafts
- industrial gearbox and reducer shafts
- conveyor pulley and elevator drum shafts
Known failure patterns
- lubricant starvation at the centre rib area when the D1/W33 groove is not connected to a relubrication supply
- pressed EA cage fatigue under sustained vibration when minimum load is not maintained
- micro-pitting when the EHL film is thinner than the raceway composite roughness
- 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
- Vibrating-duty 55 mm bearings need the right clearance class and secure fits; verify the k5/m5 seat and relubrication routing rather than assuming the open 21311K is greased for life.
- The D1/W33 groove only helps if the housing has a matching grease passage; mounting a grooved 21311K in a solid block with no port wastes the feature and leaves the centre rows under-lubricated.
- Open spherical rollers swallow dust in mining duty; specify labyrinth or taconite seals externally, or the 3,700 r/min grease rating is lost to abrasive wear long before fatigue.
- Oil relubrication toward 4,800 r/min needs drain and level design; flooding the 29 mm cavity churns heat through the heavy roller set and cage despite the higher oil speed figure.
- Do not confuse EA and EM at the same number: 21311K carries C design-code; swapping to the other cage execution changes mass, speed behaviour and sometimes suitability for vibration, even though the 55×120 mm envelope is identical.
- The 161/163 kN ratings, 16.1 kN Pu and 1690 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for 21311K (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 21311K?
21311K is an NTN double-row spherical roller bearing to ISO 15: 55 mm bore, 120 mm OD and 29 mm width (2.165 × 4.724 × 1.142 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 161 kN, C0 163 kN, Pu 16.1 kN, grease limiting speed 3,700 r/min, oil 4,800 r/min, mass about 1690 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. 21311K 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 21311.
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. 21311K is the C design-code execution.
What do D1 and W33 mean on 21311K?
21311K 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 21311K 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 — 161 kN C / 163 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.