31321XU bearing: complete specifications & equivalents
The 31321XU is a ISO 355 radial bearing sized 105 x 225 x 58 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 | 58 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 420 kN |
| Basic static load rating C0 | 470 kN |
| Fatigue load limit Pu | 49 kN |
| Limiting speed (mechanical) | 1700 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 9650 g |
| Manufacturer designation | NTN 31321XU |
| 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 & 31300-series range
| Bore d | 4.134 in |
|---|---|
| Outer diameter D | 8.858 in |
| Width B | 2.283 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 60 mm |
| Smallest bore in 31300-series | 25 mm |
| Largest outer diameter in 31300-series | 320 mm |
| Width range across 31300-series | 18.25–82 mm |
| Bore position in 31300-series (smallest first) | 17 of 22 |
| Bore above smallest 31300-series size | 80 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 31321XU | 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 31321XU model number is decoded
In NTN Ball and Roller Bearings CAT.No.2203E, the NTN order number 31321XU denotes the steep-angle 31300 family for high axial load share of metric tapered roller bearings, 105 mm bore, 225 mm outside diameter and 58 mm assembled width T (4.134 × 8.858 × 2.283 in) to the ISO 355 boundary plan. NTN also quotes this bearing with its ISO 355 dimension-series abbreviation, 7GB, which is the maker-neutral cross-reference for the 105×225 mm envelope; 4T is NTN's own tapered-roller brand mark on the parts. A tapered roller bearing reacts combined radial and one-direction axial load; NTN mounts 31321XU cone and cup separately and adjusts end play or preload against a second bearing, so the arrangement locates the shaft in both directions. Imperial cross-check for the drawing: 105×225×58 mm is 4.134 × 8.858 × 2.283 in; ISO 355 makes the envelope interchangeable but C/C0, 420/470 kN, is NTN-specific. 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 31321XU.
Typical equipment & failure modes
Common applications
- paper-machine press-section rolls
- large agricultural and forestry machine axles
- heavy industrial gearboxes and crane travel drives
- rolling-mill auxiliary and pinion-stand shafts
Known failure patterns
- cone-raceway spalling at the large rib when preload is set too high for the lubricant film
- preload loss from racewear when one bearing of the paired set is replaced without re-adjusting end play
- rib scoring when axial load is carried beyond the cone rib capacity of the adjusted pair
- cage damage from a mounting blow delivered through the roller complement instead of the ring face
- fretting corrosion on a loose cone seat that creeps under rotating load
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 9650 g ring mass makes cocking during fitting a direct raceway-brinelling risk.
- The steeper contact angle of the steep-angle 31300 family for high axial load share 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.
- Grease packs must leave free volume in the 58 mm-wide set; over-greasing a paired bearing churning at the 2,300 r/min oil-band speed raises temperature and destroys the preload setting.
- Grease packs must leave free volume in the 58 mm-wide set; over-greasing a paired bearing churning at the 2,300 r/min oil-band speed raises temperature and destroys the preload setting.
- Do not confuse T (58 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 420/470 kN ratings and 49 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 31321XU (ISO 355 7GB); 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 31321XU?
31321XU is a metric 4T tapered roller bearing to ISO 355: 105 mm bore, 225 mm outside diameter and 58 mm assembled width T (4.134 × 8.858 × 2.283 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 420 kN, C0 470 kN, Pu 49 kN, grease limiting speed 1,700 r/min, oil speed 2,300 r/min, mass about 9650 g. It is an open, separable cone/cup bearing with a pressed-steel cage.
What does the 4T prefix mean on 31321XU?
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 (31321XU); the lower-case 4t- factory spelling of the code is retained among the search aliases.
How does the 31321XU designation encode the 105 mm bore and what is 7GB?
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 58 mm assembled T follow the ISO 355 dimension-series plan. 7GB 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 31321XU 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 31321XU 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 31321XU mean?
Suffix reading on 31321XU: XU combines the X ISO boundary section with the U uprated internal design; 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.