30321U bearing: complete specifications & equivalents
The 30321U is a ISO 355 radial bearing sized 105 x 225 x 53.5 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 105 mm |
| Outer diameter D | 225 mm |
| Width B | 53.5 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 485 kN |
| Basic static load rating C0 | 535 kN |
| Fatigue load limit Pu | 56 kN |
| Limiting speed (mechanical) | 1700 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 9370 g |
| Manufacturer designation | NTN 30321U |
| 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 | 4.134 in |
|---|---|
| Outer diameter D | 8.858 in |
| Width B | 2.106 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 60 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) | 20 of 32 |
| Bore above smallest 30300-series size | 90 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 30321U | 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 30321U model number is decoded
NTN supplies this 105 mm bore tapered roller position as 30321U: one cone assembly, one cup, line-contact rollers and a steel cage, rated 485 kN basic dynamic and 535 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 30321U resolves to 105 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. NTN grades 4T metric bearings as open bearings without integral seals; at 105 mm bore the application supplies the seals and the grease fill or oil supply to the 2GB ISO 355 assembly. Speed planning uses both catalogue columns: grease 1,700 r/min is the cage/rib mechanical ceiling for 30321U, oil 2,300 r/min is available with circulating oil — a 600 r/min margin at this size. Mount the 105 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 30321U.
Typical equipment & failure modes
Common applications
- marine winch and deck-machinery shafts
- paper-machine press-section rolls
- large agricultural and forestry machine axles
- heavy industrial gearboxes and crane travel drives
Known failure patterns
- cup creep and housing fretting when the specified outer-ring press fit is not achieved
- flaking on one cone only when a back-to-back / face-to-face pair is loaded unevenly by a bent shaft
- smearing on the roller large ends and cone rib after a dry start with preload but no oil film
- 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
- Mount the 105 mm cone by induction heating (max 120 °C) and the cup with a press sleeve; the 9370 g ring mass makes cocking during fitting a direct raceway-brinelling risk.
- 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 105 mm bore; do not swap to the lighter family without re-checking the 1,700 r/min grease limit and the thrust load split.
- The 60.0 mm section leaves little room for an oversized shaft fillet; check the mounting-chamfer table for 30321U or the ring will bottom out on the radius instead of the shoulder face.
- The 60.0 mm section leaves little room for an oversized shaft fillet; check the mounting-chamfer table for 30321U or the ring will bottom out on the radius instead of the shoulder face.
- The 60.0 mm section leaves little room for an oversized shaft fillet; check the mounting-chamfer table for 30321U or the ring will bottom out on the radius instead of the shoulder face.
- The 485/535 kN ratings and 56 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 30321U (ISO 355 2GB); 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 30321U?
30321U is a metric 4T tapered roller bearing to ISO 355: 105 mm bore, 225 mm outside diameter and 53.5 mm assembled width T (4.134 × 8.858 × 2.106 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 485 kN, C0 535 kN, Pu 56 kN, grease limiting speed 1,700 r/min, oil speed 2,300 r/min, mass about 9370 g. It is an open, separable cone/cup bearing with a pressed-steel cage.
What does the 4T prefix mean on 30321U?
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 (30321U); the lower-case 4t- factory spelling of the code is retained among the search aliases.
How does the 30321U designation encode the 105 mm bore and what is 2GB?
last two digits 21 are the ISO bore code, ×5 = 105 mm (codes 00–03 use the 10/12/15/17 exception table). The 225 mm OD and 53.5 mm assembled T follow the ISO 355 dimension-series plan. 2GB 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 30321U list two speeds, 1,700 and 2,300 r/min?
The lower figure, 1,700 r/min, is the grease-lubricated limiting speed — the mechanical ceiling for the cage, rollers and cone-rib contact. With oil lubrication NTN rates 30321U at 2,300 r/min because oil removes rib-contact heat better. Real limits still depend on preload, oil flow and cooling.
What does the suffix on 30321U mean?
Suffix reading on 30321U: U marks the reinforced/uprated internal design of the bare number, a separate order number with higher load capacity than the basic execution; 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.