NKX25-Z bearing: complete specifications & equivalents
The NKX25-Z is a DIN 616 radial bearing sized 25 x 37 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 | 25 mm |
| Outer diameter D | 37 mm |
| Width B | 30 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 19 kN |
| Basic static load rating C0 | 32.5 kN |
| Fatigue load limit Pu | 4 kN |
| Reference speed (thermal) | 6300 rpm |
| Limiting speed (mechanical) | 5500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 130 g |
| Manufacturer designation | NKX 25 Z |
| Standard | DIN 616 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.9 needle roller / thrust ball, caged thrust part |
| Last verified | 2026-09-26 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.9 needle roller / thrust ball, caged thrust part) · extracted 2026-09-26
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.9 needle roller / thrust ball, caged thrust part); 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 & NKX-series range
| Bore d | 0.984 in |
|---|---|
| Outer diameter D | 1.457 in |
| Width B | 1.181 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 6 mm |
| Smallest bore in NKX-series | 10 mm |
| Largest outer diameter in NKX-series | 85 mm |
| Width range across NKX-series | 23–40 mm |
| Bore position in NKX-series (smallest first) | 6 of 13 |
| Bore above smallest NKX-series size | 15 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| NKX25 | SKF | full Dimensions and internal design equivalent — standard interchange. | Same 25×37×30 mm envelope and equivalent catalogue ratings; NKX25 is the combined needle/thrust ball execution — boundary-dimension interchangeable, execution differences (seals, shields, cage) apply. |
| RNA6904 | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 25×37×30 mm envelope, but catalogue C/C0 differ between the executions (19/32.5 vs 35.2/53 kN) — boundary dimensions match, not a load-rating equivalent. |
| NX25-Z | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 25×37×30 mm envelope, but catalogue C/C0 differ between the executions (19/32.5 vs 15.1/24.5 kN) — boundary dimensions match, not a load-rating equivalent. |
| NX25 | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 25×37×30 mm envelope, but catalogue C/C0 differ between the executions (19/32.5 vs 15.1/24.5 kN) — boundary dimensions match, not a load-rating equivalent. |
| NKXR25 | SKF | full Dimensions and internal design equivalent — standard interchange. | Envelope-identical (25×37×30 mm) combined needle/thrust needle execution with ratings within 10 % — substitution possible after checking ring/flange construction. |
| NKXR25-Z | SKF | full Dimensions and internal design equivalent — standard interchange. | Envelope-identical (25×37×30 mm) combined needle/thrust needle execution with ratings within 10 % — substitution possible after checking ring/flange construction. |
Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.
How the NKX25-Z model number is decoded
For a 25 mm shaft under radial plus one-direction axial load, NKX 25 Z from the combined needle roller / thrust ball bearings with caged thrust part provides both in 37×30 mm: needle roller cage below, caged thrust ball set above. The code NKX 25 Z reads as combined radial/thrust for a 25 mm shaft; the catalogue height 30 mm stacks the radial cage and the thrust set, and the 37 mm OD seats both parts in one bore. The thrust part takes axial load in one direction only; mount it facing the working load and provide a separate locating bearing for reverse events. Speed ceilings differ by part: 6,300 r/min thermal reference and 5,500 r/min limiting — the thrust element governs, since its washer faces see sliding components of contact. The caged thrust part survives moderate speed only with the Z shield intact — damaged shields admit grit straight into the ball raceways, and the narrow section leaves no margin.
Typical equipment & failure modes
Common applications
- machine tool feed spindles with one-direction thrust
- pump impeller shafts with steady axial pull
- gear pairs generating one-direction axial force
- rotary indexing tables under combined load
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
- thrust washer raceway wear from reverse axial shocks the one-direction thrust part cannot carry
Selection pitfalls — read before you substitute
- On a 25 mm seat the housing bore quality dominates life: a bore 0.02 mm out of round pinches the 37 mm ring or cup into a lobed shape, and the rollers then trace the housing's geometry error, not the design load.
- Do not interchange envelope-identical needle families blindly: NKX 25 Z shares its 25×37×30 mm outline with inner-ring and sealed siblings whose ratings differ — the family letters are part of the specification, not decoration.
- Reference and limiting speeds are different limits: the 6,300 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.
- Do not treat the axial rating 19.5 kN (Ca) as independent of radial load: the combined equivalent load formulas couple them, and a unit sized on radial life alone will spall the ball raceway first under real thrust.
- The thrust part is one-direction: reverse axial events — however brief — lift the rolling elements off the raceway, and the subsequent re-entry impact dents the washer face; mount the NKX 25 Z facing the working thrust.
- The 19/32.5 kN ratings and 130 g mass are SKF catalogue values transcribed from ch. 7.9 of PUB BU/P1 17000 (PDF table page 658); 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 NKX 25 Z?
Beyond the L10 rating, the practical limits are journal/raceway hardness for the 25 mm seat, lubricant condition at the roller ends, and contamination through open ends — the 6.0 mm radial section leaves no reserve once a raceway is dented or ribboned.
What are the dimensions and ratings of the NKX 25 Z?
A NKX 25 Z measures 25 mm bore/Fw × 37 mm outside diameter × 30 mm width (0.984 × 1.457 × 1.181 in). From SKF catalogue PUB BU/P1 17000: radial dynamic rating C 19 kN, static C0 32.5 kN, fatigue limit Pu 4 kN, limiting speed 5,500 r/min, reference speed 6,300 r/min, mass about 130 g. Axial ratings of the thrust part: dynamic Ca 19.5 kN (Ca), static C0a 40.5 kN (C0a), minimum load factor A 0.0085; the thrust set carries load in one direction only.
How is the NKX 25 Z designation read?
NKX = needle roller radial part + caged thrust ball part for a 25 mm shaft: 37 mm OD, 30 mm overall height. The caged thrust part trades some axial capacity for higher permissible speed versus NX.
Can the NKX 25 Z run on an unhardened shaft?
The radial needle part of the NKX 25 Z runs directly on the 25 mm journal — harden to 58–64 HRC and grind it. The thrust washers are integral, so no separate inner ring exists; size the shaft for the raceway tolerances in the catalogue table.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.9 needle roller / thrust ball, caged thrust part on 2026-09-26. Read our editorial & correction policy.