30305C bearing: complete specifications & equivalents
The 30305C is a ISO 355 radial bearing sized 25 x 62 x 18.25 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 25 mm |
| Outer diameter D | 62 mm |
| Width B | 18.25 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 46 kN |
| Basic static load rating C0 | 41.5 kN |
| Limiting speed (mechanical) | 6400 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 264 g |
| Manufacturer designation | NTN 30305C |
| 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 | 0.984 in |
|---|---|
| Outer diameter D | 2.441 in |
| Width B | 0.719 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 18.5 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) | 4 of 32 |
| Bore above smallest 30300-series size | 10 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 30305C | 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 30305C model number is decoded
The NTN 2203E table prints 30305C in the large-OD 30300 family with the steeper contact angle: 25 mm bore, 62 mm cup OD, 18.25 mm T, with a grease limiting speed of 6,400 r/min and an oil-lubricated ceiling of 8,500 r/min. The last two digits 05 are the ISO bore code, ×5 = 25 mm (codes 00–03 use the 10/12/15/17 exception table) under the ISO 355 numbering; the 18.25 mm value printed here is T, the width of the fully assembled cone-plus-cup set, not the inner-ring width alone. The rollers run with their large ends against the cone's integral guide rib; the rib/end-flange contact carries the thrust component and is the reason lubricant must reach the rib face of 30305C, not only the raceway. Imperial cross-check for the drawing: 25×62×18.25 mm is 0.984 × 2.441 × 0.719 in; ISO 355 makes the envelope interchangeable but C/C0, 46/41.5 kN, is NTN-specific. Re-adjustment after bedding-in is standard practice: re-check end play once the paired 30305C arrangement has run in, because initial seat seating relaxes the set preload slightly.
Typical equipment & failure modes
Common applications
- small gearbox input shafts with combined load
- scooter and light-powersport wheel and gear positions
- small conveyor pulley shafts
- steering-knuckle and kingpin positions
Known failure patterns
- cup creep and housing fretting when the specified outer-ring press fit is not achieved
- rib scoring when axial load is carried beyond the cone rib capacity of the adjusted pair
- preload loss from racewear when one bearing of the paired set is replaced without re-adjusting end play
- cage damage from a mounting blow delivered through the roller complement instead of the ring face
- indentation of the raceways by hard particles in unsealed open arrangements
Selection pitfalls — read before you substitute
- At 25 mm bore the thin section and small rollers are adjustment-sensitive: a quarter-turn of the locknut moves end play by more than on large bearings, so set the 30305C pair with a dial indicator rather than by feel.
- 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 25 mm bore; do not swap to the lighter family without re-checking the 6,400 r/min grease limit and the thrust load split.
- Do not confuse T (18.25 mm assembled width of cone + cup) with the cone width when drawing spacers; an abutment sized to T instead of the ring width leaves the cup unseated.
- ISO 355 makes the 25×62 mm envelope interchangeable but not the ratings: NTN prints 46/41.5 kN for this execution, and a cheaper same-number part can differ in roller complement and steel.
- Back-to-back and face-to-face arrangements react differently to shaft bending: pick the pair orientation for the moment load before locking the 25 mm shoulder geometry, because retrofitting flips the cups.
- The 46/41.5 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 30305C; 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 30305C?
30305C is a metric 4T tapered roller bearing to ISO 355: 25 mm bore, 62 mm outside diameter and 18.25 mm assembled width T (0.984 × 2.441 × 0.719 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 46 kN, C0 41.5 kN (2203E prints no Pu for this size), grease limiting speed 6,400 r/min, oil speed 8,500 r/min, mass about 264 g. It is an open, separable cone/cup bearing with a pressed-steel cage.
What does the 4T prefix mean on 30305C?
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 (30305C); the lower-case 4t- factory spelling of the code is retained among the search aliases.
How does the 30305C designation encode the 25 mm bore?
last two digits 05 are the ISO bore code, ×5 = 25 mm (codes 00–03 use the 10/12/15/17 exception table). The 62 mm OD and 18.25 mm assembled T follow the ISO 355 dimension-series plan.
Why does 30305C list two speeds, 6,400 and 8,500 r/min?
The lower figure, 6,400 r/min, is the grease-lubricated limiting speed — the mechanical ceiling for the cage, rollers and cone-rib contact. With oil lubrication NTN rates 30305C at 8,500 r/min because oil removes rib-contact heat better. Real limits still depend on preload, oil flow and cooling.
What does the suffix on 30305C mean?
Suffix reading on 30305C: 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.