NKX12 bearing: complete specifications & equivalents
The NKX12 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) | 13000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 38 g |
| Manufacturer designation | NKX 12 |
| 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-Z | SKF | full Dimensions and internal design equivalent — standard interchange. | Same 12×21×23 mm envelope and equivalent catalogue ratings; NKX12-Z 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 model number is decoded
SKF supplies NKX 12 for combined-load positions at moderate speed: the caged thrust balls reduce friction and allow 9,000 r/min reference where a full complement NX would overheat. Reading the designation: NKX marks needle roller + caged thrust ball, the number the 12 mm shaft seat; the 21 mm OD and 23 mm overall height come from the series plan. Execution notes: the Z suffix adds a shield over the thrust balls, TN a polymer cage; the open execution allows relubrication through the shaft, the Z execution is greased for life. Axial capability is one-direction: size the arrangement so working thrust pushes the thrust-washer face, and provide a mirrored unit or separate bearing for load reversals. 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
- 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
- grease starvation at the roller ends when relubrication intervals are stretched in dirty duty
- false brinelling of standby equipment under external vibration
- thrust-part ball or roller skidding and smearing when the axial load falls below the minimum factor
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); 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 38 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 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 have?
A NKX 12 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 13,000 r/min, reference speed 9,000 r/min, mass about 38 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 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 need a hardened and ground shaft?
The radial needle part of the NKX 12 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.