NF321 bearing: complete specifications & equivalents
The NF321 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 NF321 |
| 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 & NF300-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 NF300-series | 20 mm |
| Largest outer diameter in NF300-series | 580 mm |
| Width range across NF300-series | 15–108 mm |
| Bore position in NF300-series (smallest first) | 18 of 32 |
| Bore above smallest NF300-series size | 85 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| NF321 | 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 NF321 model number is decoded
The NTN order number NF321 denotes a 105×225×49 mm (4.134 × 8.858 × 1.929 in) cylindrical roller bearing in the NF300 family, a pressed sheet-steel cage. Reading the code: NF for the rib-on-each-ring type, then the ISO 15 diameter/width series and the bore code — ×5 = 105 mm (00–03 use the 10/12/15/17 exception table). NTN ships these bearings open with normal (CN) radial clearance and P0 tolerance as standard; precision classes and C3/C4 clearance are separate order suffixes, not part of NF321. Equivalent-load planning treats NF321 as a pure radial bearing: keep P below 355 kN at the required L10, and let a paired angular-contact or thrust part carry any sustained axial component. Housing and shaft fillets must clear the ring chamfers of NF321; an oversized radius locks the ring on its face and tilts the 49 mm-wide seat.
Typical equipment & failure modes
Common applications
- heavy industrial gearbox and reducer shafts
- large pump, turbine and compressor rotors
- rolling-mill auxiliary drive shafts
- crusher and vibrating-screen drive shafts
Known failure patterns
- roller smearing (microwelding) at start-up before the oil film builds under insufficient radial load
- pressed-steel cage pocket wear when rollers skid at light load or too-thin lubricant
- micro-pitting when the EHL film falls below the composite roughness at high specific load
- rolling-contact fatigue after the catalogue L10 life is exceeded
- fretting corrosion on a loose rotating shaft seat
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 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 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 NF321 as printed, not to the bare size.
- 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 355/360 kN ratings, 37.5 kN Pu and 8330 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for NF321 (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 NF321?
NF321 is an NTN NF 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. NF321 is one integral rib on each ring — separable inner ring with single-direction axial guidance and a defined shaft position.
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. NF321 is supplied in the standard open execution shown in the table.
Can NF321 take axial load and locate a shaft?
the NF design gives one-direction axial guidance via its single outer-ring rib. 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 NF321?
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.