31324XU bearing: complete specifications & equivalents
The 31324XU is a ISO 355 radial bearing sized 120 x 260 x 68 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 120 mm |
| Outer diameter D | 260 mm |
| Width B | 68 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 570 kN |
| Basic static load rating C0 | 655 kN |
| Fatigue load limit Pu | 66 kN |
| Limiting speed (mechanical) | 1500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 15200 g |
| Manufacturer designation | NTN 31324XU |
| 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 | 4.724 in |
|---|---|
| Outer diameter D | 10.236 in |
| Width B | 2.677 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 70 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) | 19 of 22 |
| Bore above smallest 31300-series size | 95 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 31324XU | 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 31324XU model number is decoded
31324XU is a metric single-row tapered roller bearing in the NTN 4T programme: a pressed-steel cage guides profiled rollers between a separable cone and cup on the 120×260 mm ISO 355 envelope, with 68 mm overall assembled width T. NTN also quotes this bearing with its ISO 355 dimension-series abbreviation, 7GB, which is the maker-neutral cross-reference for the 120×260 mm envelope; 4T is NTN's own tapered-roller brand mark on the parts. The printed contact-angle geometry gives the steep-angle 31300 family for high axial load share its characteristic load split — at 570/655 kN (C/C0) the static rating is about 1.15× C, typical of tapered bearings proportioned for heavy combined duty. Imperial cross-check for the drawing: 120×260×68 mm is 4.724 × 10.236 × 2.677 in; ISO 355 makes the envelope interchangeable but C/C0, 570/655 kN, is NTN-specific. Re-adjustment after bedding-in is standard practice: re-check end play once the paired 31324XU arrangement has run in, because initial seat seating relaxes the set preload slightly.
Typical equipment & failure modes
Common applications
- rolling-mill roll-neck and gearbox positions
- large crusher and SAG/AG-mill drive shafts
- wind-turbine gearbox and main-shaft arrangements
- offshore crane and drawworks drums
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
- pressed-steel cage pocket wear from roller skid at light radial load and high speed
- fretting corrosion on a loose cone seat that creeps under rotating load
Selection pitfalls — read before you substitute
- At 120 mm bore the 31324XU set is adjusted with hydraulic nuts on large mill and wind positions; follow the drive-up angle/end-play procedure, because manual torque methods cannot control preload at the 570 kN C level.
- 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 120 mm bore; do not swap to the lighter family without re-checking the 1,500 r/min grease limit and the thrust load split.
- Never fit the 120 mm cone by hammering the 260 mm cup: force for both press fits goes through the ring faces only, or brinell marks release as noise within the first running hours.
- Replacing one half of an adjusted pair without resetting end play negates the 68 mm T dimension logic: re-adjust the set and re-verify the contact pattern rather than reusing the old spacer stack.
- Minimum load matters at high speed: an unloaded 31324XU at a large fraction of 1,500 r/min lets rollers skid and smear the cone rib; spring-preload lightly loaded pair arrangements.
- The 570/655 kN ratings and 66 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 31324XU (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 31324XU?
31324XU is a metric 4T tapered roller bearing to ISO 355: 120 mm bore, 260 mm outside diameter and 68 mm assembled width T (4.724 × 10.236 × 2.677 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 570 kN, C0 655 kN, Pu 66 kN, grease limiting speed 1,500 r/min, oil speed 2,000 r/min, mass about 15200 g. It is an open, separable cone/cup bearing with a pressed-steel cage.
What does the 4T prefix mean on 31324XU?
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 (31324XU); the lower-case 4t- factory spelling of the code is retained among the search aliases.
How does the 31324XU designation encode the 120 mm bore and what is 7GB?
last two digits 24 are the ISO bore code, ×5 = 120 mm (codes 00–03 use the 10/12/15/17 exception table). The 260 mm OD and 68 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 31324XU list two speeds, 1,500 and 2,000 r/min?
The lower figure, 1,500 r/min, is the grease-lubricated limiting speed — the mechanical ceiling for the cage, rollers and cone-rib contact. With oil lubrication NTN rates 31324XU at 2,000 r/min because oil removes rib-contact heat better. Real limits still depend on preload, oil flow and cooling.
What does the suffix on 31324XU mean?
Suffix reading on 31324XU: 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.