NK18-20 bearing: complete specifications & equivalents
The NK18-20 is a DIN 616 radial bearing sized 18 x 26 x 20 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 18 mm |
| Outer diameter D | 26 mm |
| Width B | 20 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 16.1 kN |
| Basic static load rating C0 | 23.6 kN |
| Fatigue load limit Pu | 2.85 kN |
| Reference speed (thermal) | 22000 rpm |
| Limiting speed (mechanical) | 24000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 31 g |
| Manufacturer designation | NK 18/20 |
| Standard | DIN 616 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.3 machined rings with flanges, without an inner ring |
| Last verified | 2026-09-26 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.3 machined rings with flanges, without 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. 7.3 machined rings with flanges, without 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 & NK-series range
| Bore d | 0.709 in |
|---|---|
| Outer diameter D | 1.024 in |
| Width B | 0.787 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 4 mm |
| Smallest bore in NK-series | 5 mm |
| Largest outer diameter in NK-series | 130 mm |
| Width range across NK-series | 10–40 mm |
| Bore position in NK-series (smallest first) | 12 of 46 |
| Bore above smallest NK-series size | 13 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NK18-20 model number is decoded
In SKF catalogue PUB BU/P1 17000, NK 18/20 designates a flanged, machined outer ring filled with needle rollers and a cage for a 18 mm shaft — heavier section and higher accuracy than a drawn cup, with no inner ring so the journal is the raceway. In SKF nomenclature NK families drop the inner ring: the numbers after the letters give the 18 mm under-roller diameter and the 20 mm width, with the 26 mm outside diameter set by the machined-ring needle roller bearings without inner ring plan. Execution notes: the outer ring flanges are rolled from the ring material (no loose ribs to dislodge), the roller set is caged for low friction, and the TN option swaps in a polymer cage for quieter running. Speed planning separates the two ceilings: 22,000 r/min thermal reference and 24,000 r/min mechanical limiting — needle bearings tolerate high rpm only with adequate lubricant film at the 18 mm seat. Fit the outer ring with a press and a fitting sleeve, not by hammering the flanges — rolled flanges chip; the 26 mm ground OD takes the press fit that prevents outer-ring creep in oscillating duty.
Typical equipment & failure modes
Common applications
- gearbox planetary and idler gears on hardened pins
- piston-pin style pivots in hydraulic pumps
- guide rollers running on hardened tracks
- swing arms and lever pivots with oscillating duty
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
- rapid raceway scoring when the shaft journal hardness drops below 58 HRC or the ground finish wears away
Selection pitfalls — read before you substitute
- On a 18 mm seat the housing bore quality dominates life: a bore 0.02 mm out of round pinches the 26 mm ring or cup into a lobed shape, and the rollers then trace the housing's geometry error, not the design load.
- Reference and limiting speeds are different limits: the 22,000 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 18 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 16.1/23.6 kN ratings and 31 g mass are SKF catalogue values transcribed from ch. 7.3 of PUB BU/P1 17000 (PDF table page 626); combined-type axial ratings appear in the text above because the structured record carries radial values only.
Frequently asked questions
Is the NK 18/20 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 NK 18/20 have?
A NK 18/20 measures 18 mm bore/Fw × 26 mm outside diameter × 20 mm width (0.709 × 1.024 × 0.787 in). From SKF catalogue PUB BU/P1 17000: radial dynamic rating C 16.1 kN, static C0 23.6 kN, fatigue limit Pu 2.85 kN, limiting speed 24,000 r/min, reference speed 22,000 r/min, mass about 31 g.
What does NK 18/20 mean in SKF part numbering?
NK names a machined-ring needle roller bearing without inner ring: the figures give Fw 18 mm and width 20 mm, OD 26 mm comes from the dimension series, and the flanged outer ring retains the caged rollers.
Does the NK 18/20 need a hardened and ground shaft?
No. In this execution the 18 mm shaft journal is the inner raceway: it must be ground and hardened to 58–64 HRC (with matching housing bore quality on the outside). If the shaft cannot meet that, order the inner-ring sibling (NKI/NA execution) plus its ground inner ring instead.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.3 machined rings with flanges, without an inner ring on 2026-09-26. Read our editorial & correction policy.