NKI9-12 bearing: complete specifications & equivalents
The NKI9-12 is a DIN 616 radial bearing sized 9 x 19 x 12 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 9 mm |
| Outer diameter D | 19 mm |
| Width B | 12 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 6.71 kN |
| Basic static load rating C0 | 8.15 kN |
| Fatigue load limit Pu | 0.965 kN |
| Reference speed (thermal) | 26000 rpm |
| Limiting speed (mechanical) | 30000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 17 g |
| Manufacturer designation | NKI 9/12 |
| 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 | 0.354 in |
|---|---|
| Outer diameter D | 0.748 in |
| Width B | 0.472 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 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) | 4 of 30 |
| Bore above smallest NKI-series size | 4 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NKI9-12 model number is decoded
NKI 9/12 provides the full machined-ring needle roller construction: ground inner ring on a 9 mm seat, flanged outer ring at 19 mm, caged needles between them — the standard choice when a replaceable inner raceway is required. The NKI 9/12 code gives bore 9 mm and width 12 mm explicitly; unlike the RNA/NK families the shaft only needs a standard k5/j5 seat because the hardened inner ring is the raceway. The 2RS executions of the 49 series carry contact seals on both faces and a wider outer ring — their B and s dimensions differ from the open execution, so housings must be re-checked before substituting. Selection arithmetic: C 6.71 kN against C0 8.15 kN gives a C0/C ratio of 1.21, and the 0.965 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
- abrasive paste formation from dust ingressing past open ends without effective housing seals
- false brinelling of standby equipment under external vibration
- inner-ring raceway spalling after the narrow ring section runs hot with excessive interference
Selection pitfalls — read before you substitute
- On a 9 mm seat the housing bore quality dominates life: a bore 0.02 mm out of round pinches the 19 mm ring or cup into a lobed shape, and the rollers then trace the housing's geometry error, not the design load.
- Hardness is load capacity: in families without an inner ring the 9 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 6.71/8.15 kN ratings are SKF catalogue values for this exact execution (NKI 9/12); ratings can be revised without the order number changing, so keep the catalogue version (SKF catalogue PUB BU/P1 17000) with the drawing.
- The 6.71/8.15 kN ratings and 17 g mass are SKF catalogue values transcribed from ch. 7.4 of PUB BU/P1 17000 (PDF table page 638); combined-type axial ratings appear in the text above because the structured record carries radial values only.
Frequently asked questions
How is the NKI 9/12 designation read?
The letters mark a machined-ring needle roller bearing with inner ring: 9 mm bore, 12 mm width, 19 mm OD per the series plan. The hardened inner ring is the raceway, so an ordinary k5 shaft seat suffices.
Can the NKI 9/12 run on an unhardened shaft?
Yes — that is the point of this family. The NKI 9/12 carries its own hardened, ground inner ring on a 9 mm seat, so the shaft needs only a normal k5/j6 finish. The inner ring is separable and replaceable.
How should the NKI 9/12 be mounted?
Mount the inner ring on the 9 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 9/12?
Beyond the L10 rating, the practical limits are journal/raceway hardness for the 9 mm seat, lubricant condition at the roller ends, and contamination through open ends — the 5.0 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.