NUP321 bearing: complete specifications & equivalents
The NUP321 is a ISO 15 radial bearing sized 105 x 225 x 49 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 | 49 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 355 kN |
| Basic static load rating C0 | 360 kN |
| Fatigue load limit Pu | 37.5 kN |
| Limiting speed (mechanical) | 3100 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 8330 g |
| Manufacturer designation | NTN NUP321 |
| Standard | ISO 15 |
| 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 & NUP300-series range
| Bore d | 4.134 in |
|---|---|
| Outer diameter D | 8.858 in |
| Width B | 1.929 in |
| ISO bore code | 21 |
| Radial section height (D−d)/2 | 60 mm |
| Smallest bore in NUP300-series | 20 mm |
| Largest outer diameter in NUP300-series | 580 mm |
| Width range across NUP300-series | 15–108 mm |
| Bore position in NUP300-series (smallest first) | 18 of 32 |
| Bore above smallest NUP300-series size | 85 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| NUP321 | 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 NUP321 model number is decoded
NUP321 is an NTN NUP cylindrical roller bearing: the NJ rib arrangement plus a loose L-shaped rib ring on the inner ring — it locates the shaft in both axial directions, inside the 105×225×49 mm ISO 15 envelope. Numbering ties NUP321 to its envelope: type code NUP, series NUP300, 105 mm bore; the 225×49 mm outline therefore swaps dimensionally with other ISO 15 bearings of the same code, though rib arrangements differ by prefix. the bare number is the standard-capacity open execution with the normal pressed-steel cage; quote the full NUP321 designation when purchasing. Thermal planning around the 3,100 r/min grease ceiling should include the cage type (a pressed sheet-steel cage) and oil-flow option to 3,700 r/min for continuously high-duty 105 mm positions. Mount the separable inner ring + roller assembly on the shaft first and slide the outer ring into the housing; never press the outer ring through the rollers of NUP321.
Typical equipment & failure modes
Common applications
- marine gearbox and deck-machinery shafts
- large electric-motor and generator rotors
- cement and mining conveyor drive pulleys
- heavy industrial gearbox and reducer shafts
Known failure patterns
- inner-ring raceway spalling from overload in the line-contact Hertzian zone
- pressed-steel cage pocket wear when rollers skid at light load or too-thin lubricant
- grease starvation and cage drag when relubrication intervals are extended past the grease life
- false brinelling on standby machines exposed to external vibration
- edge loading from shaft deflection beyond the 3–4 arc-minute alignment limit
Selection pitfalls — read before you substitute
- Induction-heat the 105 mm inner ring (max 120 °C) and mount it before fitting the outer ring; the ring mass makes square guidance essential — driving through the rollers brinells the 225 mm raceway.
- Never press either ring through the roller complement when fitting: mounting force goes through the ring faces, or the 225 mm race brinells and releases as vibration within hours.
- The EA high-capacity roller complement changes the load figure versus the basic execution of the same number; the 355/360 kN pair here belongs to NUP321 as printed, not to the bare size.
- Grease limiting speed 3,100 r/min and oil 3,700 r/min are different limits for NUP321: the first is the cage/lubricant mechanical ceiling, the second assumes real oil flow rather than an oil bath.
- The 49 mm width and abutment faces must be square to the axis; a tilted spacer concentrates load across the roller set and shows as uneven raceway polish on the 105 mm inner ring.
- The 355/360 kN ratings, 37.5 kN Pu and 8330 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for NUP321 (standard execution); other makes sharing the ISO 15 envelope revise internal geometry without changing the order number, so keep the 2203E reference with the specification for critical drives.
Frequently asked questions
What are the dimensions and catalogue data of NUP321?
NUP321 is an NTN NUP single-row cylindrical roller bearing to ISO 15: 105 mm bore, 225 mm OD and 49 mm width (4.134 × 8.858 × 1.929 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 355 kN, C0 360 kN, Pu 37.5 kN, grease limiting speed 3,100 r/min, oil 3,700 r/min, mass about 8330 g. It is open, with a pressed sheet-steel cage.
What is the difference between NU, NJ, NUP, N and NF cylindrical roller bearings?
The prefix states the rib arrangement: NU has two outer-ring ribs and a ribless inner ring (float, no axial load); NJ adds ribs for one-direction location; NUP adds a loose L-ring to locate both directions; N has two inner-ring ribs and a separable outer ring; NF has one rib per ring for one-direction guidance. NUP321 is the NJ rib arrangement plus a loose L-shaped rib ring on the inner ring — it locates the shaft in both axial directions.
What do the EA, E and ＊ suffixes mean on NTN cylindrical roller bearings?
EA is NTN's high-capacity design with a pressed sheet-steel cage and optimised roller complement in the same ISO 15 envelope; E marks the high-capacity design at the larger bores; the ＊ symbol printed before the code in the NTN catalogue marks the ULTAGE new-generation specification and is not typed as part of the order number. NUP321 is supplied in the standard open execution shown in the table.
Can NUP321 take axial load and locate a shaft?
the NUP design provides two-direction axial location via its loose rib ring, for light/moderate thrust guidance. The loose rib ring still only suits light/short-duration axial guidance; heavy thrust belongs to a dedicated thrust bearing.
What do Fw and Ew mean for NUP321?
Fw is the inner sub-assembly raceway/roller-set envelope diameter and Ew the outer-ring raceway diameter printed for geometric checks: Fw 135 mm, Ew 195 mm. The nominal bore/OD remain 105/225 mm; Fw/Ew describe the rolling-contact path, and speeds still run to 3,100 r/min grease / 3,700 r/min oil.
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.