30311-NTN bearing: complete specifications & equivalents
The 30311-NTN is a ISO 355 radial bearing sized 55 x 120 x 31.5 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 55 mm |
| Outer diameter D | 120 mm |
| Width B | 31.5 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 172 kN |
| Basic static load rating C0 | 179 kN |
| Limiting speed (mechanical) | 3300 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1650 g |
| Manufacturer designation | NTN 30311 |
| 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 | 2.165 in |
|---|---|
| Outer diameter D | 4.724 in |
| Width B | 1.24 in |
| ISO bore code | 11 |
| Radial section height (D−d)/2 | 32.5 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) | 10 of 32 |
| Bore above smallest 30300-series size | 40 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 30311 | 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. |
| 30311-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 30311-NTN model number is decoded
NTN supplies this 55 mm bore tapered roller position as 30311: one cone assembly, one cup, line-contact rollers and a steel cage, rated 172 kN basic dynamic and 179 kN static on the large-OD 30300 family with the steeper contact angle. Reading the designation: the leading five digits follow the ISO 355 metric plan (dimension family plus two-digit bore code), and 30311 resolves to 55 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. At 172 kN C the bearing offers about 3.1 kN of dynamic capacity per millimetre of the 55 mm bore — compare any substitution on this ratio and the 31.5 mm assembled T, not on bore alone. The two speed columns differ by a factor of .75 (grease/limiting 3,300 vs oil 4,400 r/min); heat generation at the cone rib decides which lubrication a real 30311 arrangement can sustain. Mount the 55 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 30311.
Typical equipment & failure modes
Common applications
- bevel and helical pinion drives with high thrust component
- pump and compressor drive shafts carrying combined load
- machine-tool gearbox and headstock shafts
- axle final-drive and differential 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 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 55 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 30311.
- 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 55 mm bore; do not swap to the lighter family without re-checking the 3,300 r/min grease limit and the thrust load split.
- Do not confuse T (31.5 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 32.5 mm section leaves little room for an oversized shaft fillet; check the mounting-chamfer table for 30311 or the ring will bottom out on the radius instead of the shoulder face.
- Open 30311 units have no seals: a wheel-hub or gearbox application needs external sealing or the 3,300 r/min grease figure is meaningless once water reaches the cone rib.
- The 172/179 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 30311 (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 30311?
30311 is a metric 4T tapered roller bearing to ISO 355: 55 mm bore, 120 mm outside diameter and 31.5 mm assembled width T (2.165 × 4.724 × 1.24 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 172 kN, C0 179 kN (2203E prints no Pu for this size), grease limiting speed 3,300 r/min, oil speed 4,400 r/min, mass about 1650 g. It is an open, separable cone/cup bearing with a pressed-steel cage.
What does the 4T prefix mean on 30311?
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 (30311); the lower-case 4t- factory spelling of the code is retained among the search aliases.
How does the 30311 designation encode the 55 mm bore and what is 2FB?
last two digits 11 are the ISO bore code, ×5 = 55 mm (codes 00–03 use the 10/12/15/17 exception table). The 120 mm OD and 31.5 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 30311 list two speeds, 3,300 and 4,400 r/min?
The lower figure, 3,300 r/min, is the grease-lubricated limiting speed — the mechanical ceiling for the cage, rollers and cone-rib contact. With oil lubrication NTN rates 30311 at 4,400 r/min because oil removes rib-contact heat better. Real limits still depend on preload, oil flow and cooling.
What does the suffix on 30311 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.