30306-NTN bearing: complete specifications & equivalents
The 30306-NTN 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 | 66.5 kN |
| Basic static load rating C0 | 61 kN |
| Limiting speed (mechanical) | 5700 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 404 g |
| Manufacturer designation | NTN 30306 |
| 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 | 06 |
| 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 |
|---|---|---|---|
| 30306 | SKF | full Dimensions and internal design equivalent — standard interchange. | Identical ISO 15 envelope, seal and ratings band — standard interchange; re-verify precision class and clearance per supplier. |
| 30306-DF | SKF | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | Model-number interchange per ISO 15; confirm dimensions, sealing and ratings in the supplier catalogue. |
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 30306-NTN model number is decoded
For a 30 mm shaft with a thrust component, NTN lists 30306, a metric 4T tapered roller bearing of 66.5 kN C and 61 kN C0 inside the 72 mm OD, 20.75 mm-wide assembled set. On the NTN nameplate the parts carry 4T plus the bare code, while 2203E orders 30306 by the metric ISO 355 number (ISO series abbreviation 2FB): 30 mm bore, 72 mm OD. At 66.5 kN C the bearing offers about 2.2 kN of dynamic capacity per millimetre of the 30 mm bore — compare any substitution on this ratio and the 20.75 mm assembled T, not on bore alone. Grease relubrication at 5,700 r/min limiting speed targets the rib contact; if the drive needs 7,600 r/min it must be arranged for oil lubrication with a defined flow to the large roller ends. Mount the 30 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 30306.
Typical equipment & failure modes
Common applications
- pump and compressor drive shafts carrying combined load
- machine-tool gearbox and headstock shafts
- axle final-drive and differential positions
- construction-equipment wheel and pivot hubs
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
- indentation of the raceways by hard particles in unsealed open arrangements
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 30306.
- 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 5,700 r/min grease limit and the thrust load split.
- The 21.0 mm section leaves little room for an oversized shaft fillet; check the mounting-chamfer table for 30306 or the ring will bottom out on the radius instead of the shoulder face.
- Grease packs must leave free volume in the 20.75 mm-wide set; over-greasing a paired bearing churning at the 7,600 r/min oil-band speed raises temperature and destroys the preload setting.
- Open 30306 units have no seals: a wheel-hub or gearbox application needs external sealing or the 5,700 r/min grease figure is meaningless once water reaches the cone rib.
- The 66.5/61 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 30306 (ISO 355 2FB); 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 30306?
30306 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 66.5 kN, C0 61 kN (2203E prints no Pu for this size), grease limiting speed 5,700 r/min, oil speed 7,600 r/min, mass about 404 g. It is an open, separable cone/cup bearing with a pressed-steel cage.
What does the 4T prefix mean on 30306?
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 (30306); the lower-case 4t- factory spelling of the code is retained among the search aliases.
How does the 30306 designation encode the 30 mm bore and what is 2FB?
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. 2FB 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 30306 list two speeds, 5,700 and 7,600 r/min?
The lower figure, 5,700 r/min, is the grease-lubricated limiting speed — the mechanical ceiling for the cage, rollers and cone-rib contact. With oil lubrication NTN rates 30306 at 7,600 r/min because oil removes rib-contact heat better. Real limits still depend on preload, oil flow and cooling.
What does the suffix on 30306 mean?
It is the basic open 4T execution — steel cage, adjusted mounting, no seal or feature suffix. NTN uses U for the uprated design, UTG for ULTAGE large-bearing specs, X for the ISO boundary section, and C/CA/D/A for contact-angle or internal-design variants; all are separate order numbers.
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.