NKI42-20 bearing: complete specifications & equivalents
The NKI42-20 is a DIN 616 radial bearing sized 42 x 57 x 20 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 42 mm |
| Outer diameter D | 57 mm |
| Width B | 20 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 29.2 kN |
| Basic static load rating C0 | 61 kN |
| Fatigue load limit Pu | 7.65 kN |
| Reference speed (thermal) | 8500 rpm |
| Limiting speed (mechanical) | 10000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 140 g |
| Manufacturer designation | NKI 42/20 |
| Standard | DIN 616 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.4 machined rings with flanges, with an inner ring |
| Last verified | 2026-09-26 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.4 machined rings with flanges, with an inner ring) · extracted 2026-09-26
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.4 machined rings with flanges, with an inner ring); 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 & NKI-series range
| Bore d | 1.654 in |
|---|---|
| Outer diameter D | 2.244 in |
| Width B | 0.787 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 7.5 mm |
| Smallest bore in NKI-series | 5 mm |
| Largest outer diameter in NKI-series | 130 mm |
| Width range across NKI-series | 12–40 mm |
| Bore position in NKI-series (smallest first) | 18 of 30 |
| Bore above smallest NKI-series size | 37 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NKI42-20 model number is decoded
In SKF catalogue PUB BU/P1 17000, NKI 42/20 denotes a complete needle roller bearing for a 42 mm shaft — machined inner and outer rings, integral flanges on the outer ring retaining the roller set, 57 mm OD and 20 mm width. The NKI 42/20 code gives bore 42 mm and width 20 mm explicitly; unlike the RNA/NK families the shaft only needs a standard k5/j5 seat because the hardened inner ring is the raceway. Execution notes: the inner ring is ground on bore and raceway, so the shaft seat is a normal k5/j6; the flanged outer ring needs no housing shoulder, and NA 49 2RS executions add seals with a wider outer ring. The 140 g catalogue mass and 7.5 mm radial section ((57−42)/2) frame a rating of about 0.70 kN dynamic per millimetre of bore — the needle construction's density advantage over ball bearings of the same envelope. For NA 49 2RS executions the wider outer ring changes the housing depth: verify the 20 mm width and s offset dimensions against the open execution before reusing an existing bore.
Typical equipment & failure modes
Common applications
- conveyor roller ends and return rollers
- agricultural implement pivots and cutter heads
- electric motor armature shafts with ground seats
- printing and paper-handling rollers
Known failure patterns
- raceway spalling once the catalogue L10 life is exceeded or after overload events
- cage pocket wear and roller skew after sustained operation with too little radial preload
- grease starvation at the roller ends when relubrication intervals are stretched in dirty duty
- electrical erosion on VFD-driven shafts without brush or insulated mounting
- inner-ring bore fretting on a loose shaft seat, migrating hard particles into the rolling contact
Selection pitfalls — read before you substitute
- At 42 mm bore, verify shaft deflection against the needle length: these rollers tolerate little edge loading, and a simply supported span between 42 mm seats can bend past the compensation range long before the load rating is exhausted.
- Oscillating pivots fail differently: rocking through a small angle concentrates wear in the same roller positions — inspect those zones, and consider rotating the assembly's clock position at service intervals.
- Contamination, not fatigue, kills most small needle bearings: with raceways this narrow, one hard particle dents a full-width line — seal the housing even when the bearing execution itself is open.
- The 29.2/61 kN ratings and 140 g mass are SKF catalogue values transcribed from ch. 7.4 of PUB BU/P1 17000 (PDF table page 642); combined-type axial ratings appear in the text above because the structured record carries radial values only.
Frequently asked questions
How is the NKI 42/20 designation read?
The letters mark a machined-ring needle roller bearing with inner ring: 42 mm bore, 20 mm width, 57 mm OD per the series plan. The hardened inner ring is the raceway, so an ordinary k5 shaft seat suffices.
Can the NKI 42/20 run on an unhardened shaft?
Yes — that is the point of this family. The NKI 42/20 carries its own hardened, ground inner ring on a 42 mm seat, so the shaft needs only a normal k5/j6 finish. The inner ring is separable and replaceable.
How should the NKI 42/20 be mounted?
Mount the inner ring on the 42 mm seat first (induction heat, max 120 °C, or press), then fit the flanged outer ring into the H7 housing bore. Verify free rotation and, for 2RS executions, check the wider outer ring against the housing depth.
What limits the service life of a NKI 42/20?
Beyond the L10 rating, the practical limits are journal/raceway hardness for the 42 mm seat, lubricant condition at the roller ends, and contamination through open ends — the 7.5 mm radial section leaves no reserve once a raceway is dented or ribboned.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.4 machined rings with flanges, with an inner ring on 2026-09-26. Read our editorial & correction policy.