NKI38-20 bearing: complete specifications & equivalents
The NKI38-20 is a DIN 616 radial bearing sized 38 x 53 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 | 38 mm |
| Outer diameter D | 53 mm |
| Width B | 20 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 27.5 kN |
| Basic static load rating C0 | 55 kN |
| Fatigue load limit Pu | 6.8 kN |
| Reference speed (thermal) | 9500 rpm |
| Limiting speed (mechanical) | 11000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 130 g |
| Manufacturer designation | NKI 38/20 |
| 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 | 1.496 in |
|---|---|
| Outer diameter D | 2.087 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) | 16 of 30 |
| Bore above smallest NKI-series size | 33 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NKI38-20 model number is decoded
NKI 38/20 is a machined-ring needle roller bearing with an inner ring: flanged outer ring plus a separate 38 mm bore inner ring, so the shaft seat needs only ordinary tolerance, as tabulated by SKF in SKF catalogue PUB BU/P1 17000. The NKI 38/20 code gives bore 38 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. Inner rings are separable: order replacement inner rings separately by d×D×B, since the outer ring and roller assembly survive journals that ruin an inner raceway. Selection arithmetic: C 27.5 kN against C0 55 kN gives a C0/C ratio of 2.00, and the 6.8 kN fatigue load limit Pu sets the floor for the adjusted-life calculation at contaminated lubrication. Because the inner ring is separable, mount it first against its shoulder, then slide the outer ring and roller set over it — the order avoids forcing rollers across the shaft threads or burrs.
Typical equipment & failure modes
Common applications
- gearbox shafts where the journal cannot be hardened on site
- wheel and lever pivots needing a replaceable inner ring
- conveyor roller ends and return rollers
- agricultural implement pivots and cutter heads
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
- false brinelling of standby equipment under external vibration
- inner-ring bore fretting on a loose shaft seat, migrating hard particles into the rolling contact
Selection pitfalls — read before you substitute
- At 38 mm bore, verify shaft deflection against the needle length: these rollers tolerate little edge loading, and a simply supported span between 38 mm seats can bend past the compensation range long before the load rating is exhausted.
- Hardness is load capacity: in families without an inner ring the 38 mm journal must hold 58–64 HRC with a ground finish; a surface that looks fine but sits at 45 HRC will rib the raceway within weeks.
- The quoted 27.5/55 kN ratings are SKF catalogue values for this exact execution (NKI 38/20); ratings can be revised without the order number changing, so keep the catalogue version (SKF catalogue PUB BU/P1 17000) with the drawing.
- The 27.5/55 kN ratings and 130 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
What limits the service life of a NKI 38/20?
Beyond the L10 rating, the practical limits are journal/raceway hardness for the 38 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.
What are the dimensions and ratings of the NKI 38/20?
A NKI 38/20 measures 38 mm bore/Fw × 53 mm outside diameter × 20 mm width (1.496 × 2.087 × 0.787 in). From SKF catalogue PUB BU/P1 17000: radial dynamic rating C 27.5 kN, static C0 55 kN, fatigue limit Pu 6.8 kN, limiting speed 11,000 r/min, reference speed 9,500 r/min, mass about 130 g.
How is the NKI 38/20 designation read?
The letters mark a machined-ring needle roller bearing with inner ring: 38 mm bore, 20 mm width, 53 mm OD per the series plan. The hardened inner ring is the raceway, so an ordinary k5 shaft seat suffices.
Can the NKI 38/20 run on an unhardened shaft?
Yes — that is the point of this family. The NKI 38/20 carries its own hardened, ground inner ring on a 38 mm seat, so the shaft needs only a normal k5/j6 finish. The inner ring is separable and replaceable.
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.