NKI50-25 bearing: complete specifications & equivalents
The NKI50-25 is a DIN 616 radial bearing sized 50 x 68 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 | 50 mm |
| Outer diameter D | 68 mm |
| Width B | 25 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 40.2 kN |
| Basic static load rating C0 | 88 kN |
| Fatigue load limit Pu | 10.8 kN |
| Reference speed (thermal) | 7500 rpm |
| Limiting speed (mechanical) | 8500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 260 g |
| Manufacturer designation | NKI 50/25 |
| 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 | 1.969 in |
|---|---|
| Outer diameter D | 2.677 in |
| Width B | 0.984 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 9 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) | 20 of 30 |
| Bore above smallest NKI-series size | 45 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NKI50-25 model number is decoded
NKI 50/25 is a machined-ring needle roller bearing with an inner ring: flanged outer ring plus a separate 50 mm bore inner ring, so the shaft seat needs only ordinary tolerance, as tabulated by SKF in SKF catalogue PUB BU/P1 17000. Reading the designation: the letters name the series with inner ring, the numbers the boundary plan — 50 mm bore (d), 25 mm width; the 68 mm OD follows the dimension series, and the inner ring is a separate ground component. 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. Speed planning separates the two ceilings: 7,500 r/min thermal reference and 8,500 r/min mechanical limiting — needle bearings tolerate high rpm only with adequate lubricant film at the 50 mm seat. Mounting: heat or press the inner ring onto the 50 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
- wheel and lever pivots needing a replaceable inner ring
- conveyor roller ends and return rollers
- agricultural implement pivots and cutter heads
- electric motor armature shafts with ground seats
Known failure patterns
- needle edge loading and raceway denting when the shaft deflects beyond the compensation range
- 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
- rolling-contact fatigue spalling after the rated L10 life
- inner-ring bore fretting on a loose shaft seat, migrating hard particles into the rolling contact
Selection pitfalls — read before you substitute
- At 50 mm bore, verify shaft deflection against the needle length: these rollers tolerate little edge loading, and a simply supported span between 50 mm seats can bend past the compensation range long before the load rating is exhausted.
- Reference and limiting speeds are different limits: the 7,500 r/min reference is the thermal criterion under load, The limiting value is mechanical; the reference value is thermal under load, and grease choice moves it substantially.
- Hardness is load capacity: in families without an inner ring the 50 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 40.2/88 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
Does the NKI 50/25 need a hardened and ground shaft?
Yes — that is the point of this family. The NKI 50/25 carries its own hardened, ground inner ring on a 50 mm seat, so the shaft needs only a normal k5/j6 finish. The inner ring is separable and replaceable.
What mounting mistakes ruin a NKI 50/25?
Mount the inner ring on the 50 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.
Is the NKI 50/25 sealed?
No — the open execution relies on housing seals; 2RS executions of the 49 series add contact seals with a wider outer ring as a separate order number.
Which dimensions does the NKI 50/25 have?
A NKI 50/25 measures 50 mm bore/Fw × 68 mm outside diameter × 25 mm width (1.969 × 2.677 × 0.984 in). From SKF catalogue PUB BU/P1 17000: radial dynamic rating C 40.2 kN, static C0 88 kN, fatigue limit Pu 10.8 kN, limiting speed 8,500 r/min, reference speed 7,500 r/min, mass about 260 g.
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.