30306D bearing: complete specifications & equivalents
The 30306D is a ISO 355 radial bearing sized 30 x 72 x 20.75 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 30 mm |
| Outer diameter D | 72 mm |
| Width B | 20.75 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 53.5 kN |
| Basic static load rating C0 | 51.5 kN |
| Limiting speed (mechanical) | 5000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 394 g |
| Manufacturer designation | NTN 30306D |
| 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 | 1.181 in |
|---|---|
| Outer diameter D | 2.835 in |
| Width B | 0.817 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 21 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) | 5 of 32 |
| Bore above smallest 30300-series size | 15 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 30306D | 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 30306D model number is decoded
In NTN Ball and Roller Bearings CAT.No.2203E, the NTN order number 30306D denotes the large-OD 30300 family with the steeper contact angle of metric tapered roller bearings, 30 mm bore, 72 mm outside diameter and 20.75 mm assembled width T (1.181 × 2.835 × 0.817 in) to the ISO 355 boundary plan. Reading the designation: the leading five digits follow the ISO 355 metric plan (dimension family plus two-digit bore code), and 30306D resolves to 30 mm bore; the NTN factory mark 4T is stamped on cone and cup but is a brand mark, not a size code, so the catalogue sku is printed without it. A tapered roller bearing reacts combined radial and one-direction axial load; NTN mounts 30306D cone and cup separately and adjusts end play or preload against a second bearing, so the arrangement locates the shaft in both directions. The 1.8 kN-per-mm-bore capacity figure for 30306D summarises the 53.5 kN rating over 30 mm bore; use it to sanity-check an interchange candidate before swapping brands. Re-adjustment after bedding-in is standard practice: re-check end play once the paired 30306D arrangement has run in, because initial seat seating relaxes the set preload slightly.
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
- 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 fatigue when the pair is run continuously near the grease limiting speed without oil cooling
- water-induced pitting when the open bearing is exposed to washdown without external seals
Selection pitfalls — read before you substitute
- Hub and pinion bearings of this 30 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 30306D.
- 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 30 mm bore; do not swap to the lighter family without re-checking the 5,000 r/min grease limit and the thrust load split.
- ISO 355 makes the 30×72 mm envelope interchangeable but not the ratings: NTN prints 53.5/51.5 kN for this execution, and a cheaper same-number part can differ in roller complement and steel.
- ISO 355 makes the 30×72 mm envelope interchangeable but not the ratings: NTN prints 53.5/51.5 kN for this execution, and a cheaper same-number part can differ in roller complement and steel.
- Do not confuse T (20.75 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.
- The 53.5/51.5 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 30306D (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 30306D?
30306D is a metric 4T tapered roller bearing to ISO 355: 30 mm bore, 72 mm outside diameter and 20.75 mm assembled width T (1.181 × 2.835 × 0.817 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 53.5 kN, C0 51.5 kN (2203E prints no Pu for this size), grease limiting speed 5,000 r/min, oil speed 6,700 r/min, mass about 394 g. It is an open, separable cone/cup bearing with a pressed-steel cage.
What does the 4T prefix mean on 30306D?
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 (30306D); the lower-case 4t- factory spelling of the code is retained among the search aliases.
How does the 30306D designation encode the 30 mm bore and what is 7FB?
last two digits 06 are the ISO bore code, ×5 = 30 mm (codes 00–03 use the 10/12/15/17 exception table). The 72 mm OD and 20.75 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 30306D list two speeds, 5,000 and 6,700 r/min?
The lower figure, 5,000 r/min, is the grease-lubricated limiting speed — the mechanical ceiling for the cage, rollers and cone-rib contact. With oil lubrication NTN rates 30306D at 6,700 r/min because oil removes rib-contact heat better. Real limits still depend on preload, oil flow and cooling.
What does the suffix on 30306D mean?
Suffix reading on 30306D: 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.