21311-NTN bearing: complete specifications & equivalents
The 21311-NTN 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 | 1710 g |
| Manufacturer designation | NTN 21311 |
| 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 | 11 |
| 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 |
|---|---|---|---|
| 21311K | 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 21311K (K/K30 sleeve or tapered-seat mounting). Verify shaft arrangement. |
| 21311 | SKF | full Dimensions and internal design equivalent — standard interchange. | Identical ISO 15 envelope, seal and ratings band — standard interchange; re-verify precision class and clearance per supplier. |
| 21311-EK | SKF | full Dimensions and internal design equivalent — standard interchange. | Identical ISO 15 envelope, seal and ratings band — standard interchange; re-verify precision class and clearance per supplier. |
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 21311-NTN model number is decoded
For heavy radial load with misalignment on a 55 mm shaft, NTN supplies 21311: sphered outer raceway, two roller rows, pressed-steel cage of the 213-series C design, oil speed 4,800 r/min. Numbering ties 21311 to its envelope and execution: same-number EA versus EM or plain variants share the 55 mm bore but differ in cage and sometimes mass, so they are quoted as separate articles. The bearing accepts predominantly radial load with a moderate axial share, but is not a pure thrust bearing: sustained axial-only load skids the unloaded row and damages the C design-code cage. The 32.5 mm section height hosts the spherical roller geometry; shaft and housing fillet radii must clear the chamfer table so the 29 mm-wide ring seats fully on both sides. On vibrating-duty shafts verify the radial clearance class and cage choice at order time; the open 21311 leaves sealing and the C3/C4 clearance decision to the application drawing.
Typical equipment & failure modes
Common applications
- pump and fan shafts under heavy belt load
- marine propulsion auxiliary shafts
- vibrating screen and feeder shafts
- industrial gearbox and reducer 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
- false brinelling on stopped machines exposed to screen or crusher vibration
- false brinelling on stopped machines exposed to screen or crusher vibration
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 21311 is greased for life.
- Do not confuse EA and EM at the same number: 21311 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 two roller rows must share load equally — a tilted spacer or unequal abutment on the 29 mm-wide ring loads one row only and shows as asymmetric race polish during inspection.
- Never substitute 21311 by envelope alone: the 163 kN C0 and 16.1 kN Pu are specific to the NTN C design-code execution, and vibrating duty depends heavily on cage identity.
- Never substitute 21311 by envelope alone: the 163 kN C0 and 16.1 kN Pu are specific to the NTN C design-code execution, and vibrating duty depends heavily on cage identity.
- The 161/163 kN ratings, 16.1 kN Pu and 1710 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for 21311 (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 21311?
21311 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 1710 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?
21311 has a cylindrical bore and mounts directly on a machined shaft seat. Its tapered-bore counterpart is 21311K (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. 21311 is the C design-code execution.
What do D1 and W33 mean on 21311?
21311 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 21311 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.