NKX12-Z bearing: complete specifications & equivalents
The NKX12-Z is a DIN 616 radial bearing sized 12 x 21 x 23 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 12 mm |
| Outer diameter D | 21 mm |
| Width B | 23 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 9.13 kN |
| Basic static load rating C0 | 12 kN |
| Fatigue load limit Pu | 1.43 kN |
| Reference speed (thermal) | 9000 rpm |
| Limiting speed (mechanical) | 7500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 40 g |
| Manufacturer designation | NKX 12 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 | 0.472 in |
|---|---|
| Outer diameter D | 0.827 in |
| Width B | 0.906 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 4.5 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) | 2 of 13 |
| Bore above smallest NKX-series size | 2 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| NKX12 | SKF | full Dimensions and internal design equivalent — standard interchange. | Same 12×21×23 mm envelope and equivalent catalogue ratings; NKX12 is the combined needle/thrust ball execution — boundary-dimension interchangeable, execution differences (seals, shields, cage) apply. |
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 NKX12-Z model number is decoded
NKX 12 Z integrates two bearings in one envelope: needle rollers for the radial load on a 12 mm seat, and a cage-held thrust ball set for axial loads up to 10.4 kN (Ca) dynamic. In SKF nomenclature NKX is the combined family: the number states 12 mm, and unlike NX the thrust balls are caged, trading some axial capacity for speed and friction. 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. The minimum load factor A 0.0014 applies to the thrust part: below that axial load the rolling elements of the thrust set skid, so springs or preload washers are part of the arrangement, not an afterthought. Apply the working axial load after mounting and re-check running torque; a rising torque in the first minutes signals balls climbing the washer lip under reversed thrust.
Typical equipment & failure modes
Common applications
- turntable and swivel mounts
- machine tool feed spindles with one-direction thrust
- pump impeller shafts with steady axial pull
- gear pairs generating one-direction axial force
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
- abrasive paste formation from dust ingressing past open ends without effective housing seals
- electrical erosion on VFD-driven shafts without brush or insulated mounting
- thrust washer raceway wear from reverse axial shocks the one-direction thrust part cannot carry
Selection pitfalls — read before you substitute
- On a 12 mm seat the housing bore quality dominates life: a bore 0.02 mm out of round pinches the 21 mm ring or cup into a lobed shape, and the rollers then trace the housing's geometry error, not the design load.
- The quoted 9.13/12 kN ratings are SKF catalogue values for this exact execution (NKX 12 Z); ratings can be revised without the order number changing, so keep the catalogue version (SKF catalogue PUB BU/P1 17000) with the drawing.
- 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.
- Minimum axial load is a real requirement: below factor A 0.0014 the thrust elements skid, polish their raceways and lose them — springs or preload washers belong in the arrangement drawing, not the troubleshooting notes.
- Height stack-up is easy to mis-check: the thrust-washer part adds height beyond a plain needle bearing, and clamping the stack solid over it preloads the thrust set beyond its rating.
- The 9.13/12 kN ratings and 40 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
Is the NKX 12 Z sealed?
No — this execution is open and depends on the housing sealing arrangement; grease it at assembly and keep the relubrication interval short in dirty duty.
Which dimensions does the NKX 12 Z have?
A NKX 12 Z measures 12 mm bore/Fw × 21 mm outside diameter × 23 mm width (0.472 × 0.827 × 0.906 in). From SKF catalogue PUB BU/P1 17000: radial dynamic rating C 9.13 kN, static C0 12 kN, fatigue limit Pu 1.43 kN, limiting speed 7,500 r/min, reference speed 9,000 r/min, mass about 40 g. Axial ratings of the thrust part: dynamic Ca 10.4 kN (Ca), static C0a 16.6 kN (C0a), minimum load factor A 0.0014; the thrust set carries load in one direction only.
What does NKX 12 Z mean in SKF part numbering?
NKX = needle roller radial part + caged thrust ball part for a 12 mm shaft: 21 mm OD, 23 mm overall height. The caged thrust part trades some axial capacity for higher permissible speed versus NX.
Does the NKX 12 Z need a hardened and ground shaft?
The radial needle part of the NKX 12 Z runs directly on the 12 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.