NKI40-30-TN bearing: complete specifications & equivalents
The NKI40-30-TN is a DIN 616 radial bearing sized 40 x 55 x 30 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 40 mm |
| Outer diameter D | 55 mm |
| Width B | 30 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | polymer (PA66 glass-fibre reinforced) |
| Basic dynamic load rating C | 45.7 kN |
| Basic static load rating C0 | 108 kN |
| Fatigue load limit Pu | 13.7 kN |
| Reference speed (thermal) | 9000 rpm |
| Limiting speed (mechanical) | 10000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 220 g |
| Manufacturer designation | NKI 40/30 TN |
| 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 | 1.575 in |
|---|---|
| Outer diameter D | 2.165 in |
| Width B | 1.181 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) | 17 of 30 |
| Bore above smallest NKI-series size | 35 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NKI40-30-TN model number is decoded
NKI 40/30 TN is a machined-ring needle roller bearing with an inner ring: flanged outer ring plus a separate 40 mm bore inner ring, so the shaft seat needs only ordinary tolerance, as tabulated by SKF in SKF catalogue PUB BU/P1 17000. The designation NKI 40/30 TN tells you the envelope — 40×55×30 mm — and the family tells you the construction: complete bearing, replaceable inner ring, flanged outer ring retaining the needle rollers. 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 45.7 kN against C0 108 kN gives a C0/C ratio of 2.36, and the 13.7 kN fatigue load limit Pu sets the floor for the adjusted-life calculation at contaminated lubrication. For NA 49 2RS executions the wider outer ring changes the housing depth: verify the 30 mm width and s offset dimensions against the open execution before reusing an existing bore.
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
- 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 40 mm bore, verify shaft deflection against the needle length: these rollers tolerate little edge loading, and a simply supported span between 40 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 45.7/108 kN ratings and 220 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 are the dimensions and ratings of the NKI 40/30 TN?
A NKI 40/30 TN measures 40 mm bore/Fw × 55 mm outside diameter × 30 mm width (1.575 × 2.165 × 1.181 in). From SKF catalogue PUB BU/P1 17000: radial dynamic rating C 45.7 kN, static C0 108 kN, fatigue limit Pu 13.7 kN, limiting speed 10,000 r/min, reference speed 9,000 r/min, mass about 220 g.
How is the NKI 40/30 TN designation read?
The letters mark a machined-ring needle roller bearing with inner ring: 40 mm bore, 30 mm width, 55 mm OD per the series plan. The hardened inner ring is the raceway, so an ordinary k5 shaft seat suffices.
Can the NKI 40/30 TN run on an unhardened shaft?
Yes — that is the point of this family. The NKI 40/30 TN carries its own hardened, ground inner ring on a 40 mm seat, so the shaft needs only a normal k5/j6 finish. The inner ring is separable and replaceable.
How should the NKI 40/30 TN be mounted?
Mount the inner ring on the 40 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.
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.