30308C bearing: complete specifications & equivalents
The 30308C is a ISO 355 radial bearing sized 40 x 90 x 25.25 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 40 mm |
| Outer diameter D | 90 mm |
| Width B | 25.25 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 92 kN |
| Basic static load rating C0 | 87 kN |
| Limiting speed (mechanical) | 4200 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 726 g |
| Manufacturer designation | NTN 30308C |
| 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 | 1.575 in |
|---|---|
| Outer diameter D | 3.543 in |
| Width B | 0.994 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 25 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) | 7 of 32 |
| Bore above smallest 30300-series size | 25 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 30308C | 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 30308C model number is decoded
30308C belongs to the NTN metric 4T tapered roller range (large-OD 30300 family with the steeper contact angle); the open bearing leaves sealing to the application and is normally ordered and mounted as an adjustable matched pair. NTN also quotes this bearing with its ISO 355 dimension-series abbreviation which is the maker-neutral cross-reference for the 40×90 mm envelope; 4T is NTN's own tapered-roller brand mark on the parts. Suffix reading on 30308C: 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. Speed planning uses both catalogue columns: grease 4,200 r/min is the cage/rib mechanical ceiling for 30308C, oil 5,600 r/min is available with circulating oil — a 1,400 r/min margin at this size. Open 4T bearings need application seals; without them the grease at the cone rib of 30308C washes out and the rib/roller-end contact smears on the first wet or dusty shift.
Typical equipment & failure modes
Common applications
- construction-equipment wheel and pivot hubs
- truck and bus wheel hubs in paired arrangements
- industrial gearbox and speed-reducer shafts
- bevel and helical pinion drives with high thrust component
Known failure patterns
- cone-raceway spalling at the large rib when preload is set too high for the lubricant film
- 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
- cage damage from a mounting blow delivered through the roller complement instead of the ring face
- fretting corrosion on a loose cone seat that creeps under rotating load
Selection pitfalls — read before you substitute
- Hub and pinion bearings of this 40 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 30308C.
- 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 40 mm bore; do not swap to the lighter family without re-checking the 4,200 r/min grease limit and the thrust load split.
- The 25.0 mm section leaves little room for an oversized shaft fillet; check the mounting-chamfer table for 30308C or the ring will bottom out on the radius instead of the shoulder face.
- Never fit the 40 mm cone by hammering the 90 mm cup: force for both press fits goes through the ring faces only, or brinell marks release as noise within the first running hours.
- ISO 355 makes the 40×90 mm envelope interchangeable but not the ratings: NTN prints 92/87 kN for this execution, and a cheaper same-number part can differ in roller complement and steel.
- The 92/87 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 30308C; 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 30308C?
30308C is a metric 4T tapered roller bearing to ISO 355: 40 mm bore, 90 mm outside diameter and 25.25 mm assembled width T (1.575 × 3.543 × 0.994 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 92 kN, C0 87 kN (2203E prints no Pu for this size), grease limiting speed 4,200 r/min, oil speed 5,600 r/min, mass about 726 g. It is an open, separable cone/cup bearing with a pressed-steel cage.
What does the 4T prefix mean on 30308C?
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 (30308C); the lower-case 4t- factory spelling of the code is retained among the search aliases.
How does the 30308C designation encode the 40 mm bore?
last two digits 08 are the ISO bore code, ×5 = 40 mm (codes 00–03 use the 10/12/15/17 exception table). The 90 mm OD and 25.25 mm assembled T follow the ISO 355 dimension-series plan.
Why does 30308C list two speeds, 4,200 and 5,600 r/min?
The lower figure, 4,200 r/min, is the grease-lubricated limiting speed — the mechanical ceiling for the cage, rollers and cone-rib contact. With oil lubrication NTN rates 30308C at 5,600 r/min because oil removes rib-contact heat better. Real limits still depend on preload, oil flow and cooling.
What does the suffix on 30308C mean?
Suffix reading on 30308C: 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.