NU421-M bearing: complete specifications & equivalents
The NU421-M is a ISO 15 radial bearing sized 105 x 260 x 60 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 105 mm |
| Outer diameter D | 260 mm |
| Width B | 60 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | brass |
| Basic dynamic load rating C | 501 kN |
| Basic static load rating C0 | 570 kN |
| Fatigue load limit Pu | 64 kN |
| Reference speed (thermal) | 2800 rpm |
| Limiting speed (mechanical) | 3400 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 17500 g |
| Manufacturer designation | SKF NU 421 M |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 6.1 single-row cylindrical roller bearings |
| Last verified | 2026-09-26 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 6.1 single-row cylindrical roller bearings) · extracted 2026-09-26
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 6.1 single-row cylindrical roller bearings); SKF® and SKF Explorer® are trademarks of AB SKF, used here for identification only — mpnbase is not an authorized SKF distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at skf.com.
Dimensions in inches & NU400-series range
| Bore d | 4.134 in |
|---|---|
| Outer diameter D | 10.236 in |
| Width B | 2.362 in |
| ISO bore code | 21 |
| Radial section height (D−d)/2 | 77.5 mm |
| Smallest bore in NU400-series | 25 mm |
| Largest outer diameter in NU400-series | 310 mm |
| Width range across NU400-series | 21–72 mm |
| Bore position in NU400-series (smallest first) | 16 of 17 |
| Bore above smallest NU400-series size | 80 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| NU421 | 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 NU421-M model number is decoded
For a 105 mm shaft, SKF lists NU421-M as single-row caged cylindrical roller: 260 mm OD, 60 mm wide, Pu 64 kN, the catalogue lists 2,800 r/min thermal reference speed and 3,400 r/min mechanical limiting speed. Structurally, the NU design has two integral flanges on the outer ring and no flanges on the inner ring, so the inner ring together with the roller set is separable. In arrangement terms it is non-locating: the inner ring assembly can float axially in both directions and the bearing cannot support axial load. The M suffix marks the basic (non-E) execution with a machined brass cage, the standard choice for the larger and earlier-design sizes. The one-piece machined brass cage is reflected in the published speeds and temperature limits. Selection arithmetic: C0/C ≈ 1.14 (570 against 501 kN), and the Pu figure 64 kN is the fatigue load-limit floor for the SKF life equation; the catalogue lists 2,800 r/min thermal reference speed and 3,400 r/min mechanical limiting speed. Mounting: fit the inner ring and roller assembly onto the shaft and the outer ring into the housing independently; thermal expansion is absorbed by axial float, so do not trap the inner ring between shaft shoulders. A 105 mm seat normally takes a m6 interference with an H6 housing bore when the inner ring rotates.
Typical equipment & failure modes
Common applications
- heavy gearbox and pinion shafts
- large pump and blower rotors
- rolling-mill auxiliary drive shafts
- paper-machine press rolls
Known failure patterns
- inner-ring raceway spalling from overload or contamination in the line-contact hertz zone
- outer-ring raceway fatigue after extended service at loads above the catalogue L10 rating
- cage pocket wear from roller skew at light load
- cage pocket wear from roller skidding at insufficient radial load or during start-up before oil film build-up
- surface distress (micro-pitting) when the EHL film falls below the composite roughness at high specific load
- edge-loading fatigue after shaft deflection beyond the 3–4 minute alignment limit
- electrical pitting on VFD-driven shafts without grounding protection
Selection pitfalls — read before you substitute
- Do not use a NU bearing where axial load must be carried — the design carries radial load only
- The dimension series 4 (heavy-section ISO 15 envelope) envelope is shared with the N/NU/NJ/NUP executions of 421, but flange configuration and axial-locating behaviour differ — quote the full SKF NU 421 M and do not substitute rib styles without checking the shaft locating scheme.
- Catalogue reference and limiting speeds are different criteria: observe the mechanical ceiling even when thermal calculations allow more.
- Shaft and housing fillets must clear the bearing chamfers; an oversized radius tilts the 60 mm-wide ring and concentrates load.
- The 501/570 kN ratings are SKF catalogue 17000 (2018) values for the M execution; re-verify against the current catalogue for critical drives and keep the catalogue version with the specification.
Frequently asked questions
What are the dimensions and catalogue data of NU421-M?
SKF NU 421 M is a single-row caged cylindrical roller bearing with 105 mm bore, 260 mm OD and 60 mm width per ISO 15. SKF lists C 501 kN, C0 570 kN, Pu 64 kN, reference speed 2,800 r/min and limiting speed 3,400 r/min, mass about 17500 g.
What does the NU designation and M suffix mean?
The M suffix marks the basic (non-E) execution with a machined brass cage, the standard choice for the larger and earlier-design sizes. Structurally this execution has two integral flanges on the outer ring and no flanges on the inner ring, so the inner ring together with the roller set is separable.
Can NU421-M take axial load and locate the shaft?
No — the inner ring has no flanges, so the NU bearing is non-locating and carries radial load only; use NJ (one direction), NUP (both directions) or a paired thrust bearing for axial duty.
How does NU421-M compare with the other executions in the same envelope?
The N/NU/NJ/NUP executions share the ISO 15 envelope and load ratings but differ in flange arrangement and axial-locating behaviour; quote the exact order number.
What limits the service life of this bearing most often?
Line-contact fatigue above the L10 rating, cage wear at light loads and high temperatures, and edge loading from misalignment beyond about 3–4 minutes of arc are the typical failure drivers.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 6.1 single-row cylindrical roller bearings on 2026-09-26. Read our editorial & correction policy.