30311D bearing: complete specifications & equivalents
The 30311D is a ISO 355 radial bearing sized 55 x 120 x 31.5 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 | 31.5 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 146 kN |
| Basic static load rating C0 | 154 kN |
| Limiting speed (mechanical) | 2900 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1580 g |
| Manufacturer designation | NTN 30311D |
| Standard | ISO 355 |
| 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 & 30300-series range
| Bore d | 2.165 in |
|---|---|
| Outer diameter D | 4.724 in |
| Width B | 1.24 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 32.5 mm |
| Smallest bore in 30300-series | 15 mm |
| Largest outer diameter in 30300-series | 500 mm |
| Width range across 30300-series | 14.25–105 mm |
| Bore position in 30300-series (smallest first) | 10 of 32 |
| Bore above smallest 30300-series size | 40 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 30311D | ISO 15 | full Dimensions and internal design equivalent — standard interchange. | ISO 15 boundary-dimension envelope; brand-specific OEM equivalents (NSK/FAG/NTN) pending multi-source data. |
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 30311D model number is decoded
The NTN 2203E table prints 30311D in the large-OD 30300 family with the steeper contact angle: 55 mm bore, 120 mm cup OD, 31.5 mm T, with a grease limiting speed of 2,900 r/min and an oil-lubricated ceiling of 3,800 r/min. Digit by digit, the bare number identifies the large-OD 30300 family with the steeper contact angle and a bore code resolving to 55 mm; 120 mm OD and 31.5 mm assembled T are the matching ISO 355 boundary dimensions shared with other makers of the same dimension series. Suffix reading on 30311D: the trailing A/C/D (or E1) letter marks an NTN contact-angle or internal-design revision of the base number, not a seal or clearance code; the suffix is part of the order number and the variants are not interchangeable articles. Grease relubrication at 2,900 r/min limiting speed targets the rib contact; if the drive needs 3,800 r/min it must be arranged for oil lubrication with a defined flow to the large roller ends. Mount the 55 mm-bore cone on the shaft first (induction heat, max 120 °C), fit the cup square in its housing, then set preload or end play; never drive the cup home through the rollers of 30311D.
Typical equipment & failure modes
Common applications
- truck and bus wheel hubs in paired arrangements
- industrial gearbox and speed-reducer shafts
- bevel and helical pinion drives with high thrust component
- pump and compressor drive shafts carrying combined load
Known failure patterns
- cup creep and housing fretting when the specified outer-ring press fit is not achieved
- smearing on the roller large ends and cone rib after a dry start with preload but no oil film
- flaking on one cone only when a back-to-back / face-to-face pair is loaded unevenly by a bent shaft
- pressed-steel cage pocket wear from roller skid at light radial load and high speed
- edge loading when shaft deflection exceeds the few arc-minutes of misalignment the adjusted pair allows
Selection pitfalls — read before you substitute
- Hub and pinion bearings of this 55 mm bore class are commonly adjusted in pairs; verify end play against the axle drawing and re-torque after bedding-in rather than trusting the initial preload on 30311D.
- The steeper contact angle of the large-OD 30300 family with the steeper contact angle raises axial capacity but lowers the speed ceiling against a 302/322 bearing at 55 mm bore; do not swap to the lighter family without re-checking the 2,900 r/min grease limit and the thrust load split.
- The 32.5 mm section leaves little room for an oversized shaft fillet; check the mounting-chamfer table for 30311D or the ring will bottom out on the radius instead of the shoulder face.
- The U/UTG/X/C/CA/D suffix variants of a base number share the bore but not the article: ordering 30311D by size alone can deliver the wrong contact-angle execution for a pinion position.
- ISO 355 makes the 55×120 mm envelope interchangeable but not the ratings: NTN prints 146/154 kN for this execution, and a cheaper same-number part can differ in roller complement and steel.
- The 146/154 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 30311D (ISO 355 7FB); internal geometry legitimately differs between manufacturers, so re-verify ratings, adjustment and suffix before substituting another make on a rated drive.
Frequently asked questions
What are the dimensions and catalogue ratings of NTN 30311D?
30311D is a metric 4T tapered roller bearing to ISO 355: 55 mm bore, 120 mm outside diameter and 31.5 mm assembled width T (2.165 × 4.724 × 1.24 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 146 kN, C0 154 kN (2203E prints no Pu for this size), grease limiting speed 2,900 r/min, oil speed 3,800 r/min, mass about 1580 g. It is an open, separable cone/cup bearing with a pressed-steel cage.
What does the 4T prefix mean on 30311D?
4T is NTN's tapered roller bearing brand mark, stamped on the cone and cup in the factory. It identifies the NTN 4T programme and is not a dimension, so the catalogue and this page list the bare ISO 355 number (30311D); the lower-case 4t- factory spelling of the code is retained among the search aliases.
How does the 30311D designation encode the 55 mm bore and what is 7FB?
last two digits 11 are the ISO bore code, ×5 = 55 mm (codes 00–03 use the 10/12/15/17 exception table). The 120 mm OD and 31.5 mm assembled T follow the ISO 355 dimension-series plan. 7FB is the maker-neutral ISO 355 abbreviation for this dimension series (the same code other manufacturers print); 4T is NTN's own brand mark.
Why does 30311D list two speeds, 2,900 and 3,800 r/min?
The lower figure, 2,900 r/min, is the grease-lubricated limiting speed — the mechanical ceiling for the cage, rollers and cone-rib contact. With oil lubrication NTN rates 30311D at 3,800 r/min because oil removes rib-contact heat better. Real limits still depend on preload, oil flow and cooling.
What does the suffix on 30311D mean?
Suffix reading on 30311D: the trailing A/C/D (or E1) letter marks an NTN contact-angle or internal-design revision of the base number, not a seal or clearance code; the suffix is part of the order number and the variants are not interchangeable articles.
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.