30305D bearing: complete specifications & equivalents
The 30305D 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 | 45 kN |
| Basic static load rating C0 | 43.5 kN |
| Limiting speed (mechanical) | 5900 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 266 g |
| Manufacturer designation | NTN 30305D |
| 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 |
|---|---|---|---|
| 30305D | 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 30305D model number is decoded
For a 25 mm shaft with a thrust component, NTN lists 30305D, a metric 4T tapered roller bearing of 45 kN C and 43.5 kN C0 inside the 62 mm OD, 18.25 mm-wide assembled set. NTN also quotes this bearing with its ISO 355 dimension-series abbreviation, 7FB, which is the maker-neutral cross-reference for the 25×62 mm envelope; 4T is NTN's own tapered-roller brand mark on the parts. The pressed-steel cage and surface-finished roller ends are standard 4T execution; ULTAGE-marked variants use upgraded material and internal geometry aimed at longer rating life with the same ISO 355 envelope. Grease relubrication at 5,900 r/min limiting speed targets the rib contact; if the drive needs 7,800 r/min it must be arranged for oil lubrication with a defined flow to the large roller ends. Fillet radii must clear the ring chamfers of the 62 mm cup and 25 mm cone; use undercut shoulders so the rings seat fully rather than bridging on a shaft radius.
Typical equipment & failure modes
Common applications
- small conveyor pulley shafts
- steering-knuckle and kingpin positions
- small automotive wheel hubs and trailer axles
- light-vehicle differential and pinion shafts
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
- pressed-steel cage pocket wear from roller skid at light radial load and high speed
- fretting corrosion on a loose cone seat that creeps under rotating load
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 30305D 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 5,900 r/min grease limit and the thrust load split.
- The 18.5 mm section leaves little room for an oversized shaft fillet; check the mounting-chamfer table for 30305D or the ring will bottom out on the radius instead of the shoulder face.
- 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.
- Replacing one half of an adjusted pair without resetting end play negates the 18.25 mm T dimension logic: re-adjust the set and re-verify the contact pattern rather than reusing the old spacer stack.
- The 45/43.5 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 30305D (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 30305D?
30305D 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 45 kN, C0 43.5 kN (2203E prints no Pu for this size), grease limiting speed 5,900 r/min, oil speed 7,800 r/min, mass about 266 g. It is an open, separable cone/cup bearing with a pressed-steel cage.
What does the 4T prefix mean on 30305D?
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 (30305D); the lower-case 4t- factory spelling of the code is retained among the search aliases.
How does the 30305D designation encode the 25 mm bore and what is 7FB?
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. 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 30305D list two speeds, 5,900 and 7,800 r/min?
The lower figure, 5,900 r/min, is the grease-lubricated limiting speed — the mechanical ceiling for the cage, rollers and cone-rib contact. With oil lubrication NTN rates 30305D at 7,800 r/min because oil removes rib-contact heat better. Real limits still depend on preload, oil flow and cooling.
What does the suffix on 30305D mean?
Suffix reading on 30305D: 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.