32321U bearing: complete specifications & equivalents
The 32321U is a ISO 355 radial bearing sized 105 x 225 x 81.5 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 | 81.5 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 680 kN |
| Basic static load rating C0 | 825 kN |
| Fatigue load limit Pu | 87 kN |
| Limiting speed (mechanical) | 1700 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 14700 g |
| Manufacturer designation | NTN 32321U |
| 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 & 32300-series range
| Bore d | 4.134 in |
|---|---|
| Outer diameter D | 8.858 in |
| Width B | 3.209 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 60 mm |
| Smallest bore in 32300-series | 20 mm |
| Largest outer diameter in 32300-series | 460 mm |
| Width range across 32300-series | 22.25–154 mm |
| Bore position in 32300-series (smallest first) | 19 of 30 |
| Bore above smallest 32300-series size | 85 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 32321U | ISO 15 | full Dimensions and internal design equivalent — standard interchange. | ISO 15 boundary-dimension envelope; standard interchange — confirm clearance class and precision with the supplier. |
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 32321U model number is decoded
NTN supplies this 105 mm bore tapered roller position as 32321U: one cone assembly, one cup, line-contact rollers and a steel cage, rated 680 kN basic dynamic and 825 kN static on the extra-heavy 32300 family. Digit by digit, the bare number identifies the extra-heavy 32300 family and a bore code resolving to 105 mm; 225 mm OD and 81.5 mm assembled T are the matching ISO 355 boundary dimensions shared with other makers of the same dimension series. The rollers run with their large ends against the cone's integral guide rib; the rib/end-flange contact carries the thrust component and is the reason lubricant must reach the rib face of 32321U, not only the raceway. The two speed columns differ by a factor of .74 (grease/limiting 1,700 vs oil 2,300 r/min); heat generation at the cone rib decides which lubrication a real 32321U arrangement can sustain. After mounting check the contact pattern with marking blue: a pattern biased to the large or small roller end means the 105 mm pair is misadjusted and the 81.5 mm T set will edge-load in service.
Typical equipment & failure modes
Common applications
- rolling-mill auxiliary and pinion-stand shafts
- large conveyor and bucket-elevator pulleys
- mineral-processing feeder and crusher auxiliaries
- marine winch and deck-machinery shafts
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
- false brinelling on a stationary paired set exposed to external vibration
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 14700 g ring mass makes cocking during fitting a direct raceway-brinelling risk.
- The extra-heavy 32300 family at 105 mm bore (225×81.5 mm assembled) carries more capacity than the lighter 320/329 sections but generates more preload heat; confirm oil availability before running near the 2,300 r/min oil ceiling.
- Back-to-back and face-to-face arrangements react differently to shaft bending: pick the pair orientation for the moment load before locking the 105 mm shoulder geometry, because retrofitting flips the cups.
- Never fit the 105 mm cone by hammering the 225 mm cup: force for both press fits goes through the ring faces only, or brinell marks release as noise within the first running hours.
- Back-to-back and face-to-face arrangements react differently to shaft bending: pick the pair orientation for the moment load before locking the 105 mm shoulder geometry, because retrofitting flips the cups.
- The 680/825 kN ratings and 87 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 32321U (ISO 355 2GD); 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 32321U?
32321U is a metric 4T tapered roller bearing to ISO 355: 105 mm bore, 225 mm outside diameter and 81.5 mm assembled width T (4.134 × 8.858 × 3.209 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 680 kN, C0 825 kN, Pu 87 kN, grease limiting speed 1,700 r/min, oil speed 2,300 r/min, mass about 14700 g. It is an open, separable cone/cup bearing with a pressed-steel cage.
What does the 4T prefix mean on 32321U?
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 (32321U); the lower-case 4t- factory spelling of the code is retained among the search aliases.
How does the 32321U designation encode the 105 mm bore and what is 2GD?
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 81.5 mm assembled T follow the ISO 355 dimension-series plan. 2GD 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 32321U 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 32321U 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 32321U mean?
Suffix reading on 32321U: 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.