NKI55-25-TN bearing: complete specifications & equivalents
The NKI55-25-TN is a DIN 616 radial bearing sized 55 x 72 x 25 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 55 mm |
| Outer diameter D | 72 mm |
| Width B | 25 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | polymer (PA66 glass-fibre reinforced) |
| Basic dynamic load rating C | 46.8 kN |
| Basic static load rating C0 | 110 kN |
| Fatigue load limit Pu | 13.4 kN |
| Reference speed (thermal) | 6700 rpm |
| Limiting speed (mechanical) | 7500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 260 g |
| Manufacturer designation | NKI 55/25 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 | 2.165 in |
|---|---|
| Outer diameter D | 2.835 in |
| Width B | 0.984 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 8.5 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) | 21 of 30 |
| Bore above smallest NKI-series size | 50 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NKI55-25-TN model number is decoded
For a 55 mm shaft that cannot be hardened on site, NKI 55/25 TN adds a hardened, ground inner ring to the machined needle roller design: envelope 55×72×25 mm per the machined-ring needle roller bearings with inner ring plan. The NKI 55/25 TN code gives bore 55 mm and width 25 mm explicitly; unlike the RNA/NK families the shaft only needs a standard k5/j5 seat because the hardened inner ring is the raceway. TN polymer cage executions run quieter and tolerate grease-lubricated pivot duty; steel cage executions remain the choice for higher temperature or oil-bath lubrication. Minimum load matters: below roughly 0.02·C the rollers skid and smear; preloading the pivot or specifying a heavier execution avoids the glazing that pure oscillation produces on these raceways. Mounting: heat or press the inner ring onto the 55 mm k5 seat (max 120 °C), fit the flanged outer ring into the H7 housing bore, and check the 25 mm assembly for free rotation before applying load.
Typical equipment & failure modes
Common applications
- electric motor armature shafts with ground seats
- printing and paper-handling rollers
- gearbox shafts where the journal cannot be hardened on site
- wheel and lever pivots needing a replaceable inner ring
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
- rolling-contact fatigue spalling after the rated L10 life
- inner-ring raceway spalling after the narrow ring section runs hot with excessive interference
Selection pitfalls — read before you substitute
- Above 50 mm bore, thermal growth matters: the 55 mm inner ring or journal grows with temperature faster than the housing, and the small clearance of a needle roller contact leaves little reserve — check running clearance hot, not just at assembly.
- Hardness is load capacity: in families without an inner ring the 55 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 46.8/110 kN ratings are SKF catalogue values for this exact execution (NKI 55/25 TN); ratings can be revised without the order number changing, so keep the catalogue version (SKF catalogue PUB BU/P1 17000) with the drawing.
- The 46.8/110 kN ratings and 260 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 should the NKI 55/25 TN be mounted?
Mount the inner ring on the 55 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 55/25 TN?
Beyond the L10 rating, the practical limits are journal/raceway hardness for the 55 mm seat, lubricant condition at the roller ends, and contamination through open ends — the 8.5 mm radial section leaves no reserve once a raceway is dented or ribboned.
What are the dimensions and ratings of the NKI 55/25 TN?
A NKI 55/25 TN measures 55 mm bore/Fw × 72 mm outside diameter × 25 mm width (2.165 × 2.835 × 0.984 in). From SKF catalogue PUB BU/P1 17000: radial dynamic rating C 46.8 kN, static C0 110 kN, fatigue limit Pu 13.4 kN, limiting speed 7,500 r/min, reference speed 6,700 r/min, mass about 260 g.
How is the NKI 55/25 TN designation read?
The letters mark a machined-ring needle roller bearing with inner ring: 55 mm bore, 25 mm width, 72 mm OD per the series plan. The hardened inner ring is the raceway, so an ordinary k5 shaft seat suffices.
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.