NK38-20 bearing: complete specifications & equivalents
The NK38-20 is a DIN 616 radial bearing sized 38 x 48 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 | 38 mm |
| Outer diameter D | 48 mm |
| Width B | 20 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 25.5 kN |
| Basic static load rating C0 | 49 kN |
| Fatigue load limit Pu | 6.1 kN |
| Reference speed (thermal) | 11000 rpm |
| Limiting speed (mechanical) | 12000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 79 g |
| Manufacturer designation | NK 38/20 |
| 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 | 1.496 in |
|---|---|
| Outer diameter D | 1.89 in |
| Width B | 0.787 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 5 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) | 26 of 46 |
| Bore above smallest NK-series size | 33 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NK38-20 model number is decoded
Where the shaft can be hardened and ground, SKF offers NK 38/20 in the machined-ring needle roller bearings without inner ring: outer ring only, needle rollers caged between integral flanges, 38 mm bore seat and 48 mm OD. The NK 38/20 code states Fw 38 and width 20 mm directly; because the family has no inner ring, the 38 mm journal must be ground, hardened to 58–64 HRC and finished to the raceway tolerance the catalogue specifies. SKF offers this family open as standard; a matching IR inner ring can be added separately when the shaft cannot be hardened, which converts the envelope into the NKI/NA equivalent. The 79 g catalogue mass and 5.0 mm radial section ((48−38)/2) frame a rating of about 0.67 kN dynamic per millimetre of bore — the needle construction's density advantage over ball bearings of the same envelope. Mounting: the flanged outer ring presses into the H7 housing bore against its flange face; the shaft (hardened to 58–64 HRC, ground) enters afterwards, and axial retention is by the housing wall plus a cover washer.
Typical equipment & failure modes
Common applications
- piston-pin style pivots in hydraulic pumps
- guide rollers running on hardened tracks
- swing arms and lever pivots with oscillating duty
- cam followers built up from separate components
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
- grease starvation at the roller ends when relubrication intervals are stretched in dirty duty
- rolling-contact fatigue spalling after the rated L10 life
- rapid raceway scoring when the shaft journal hardness drops below 58 HRC or the ground finish wears away
Selection pitfalls — read before you substitute
- At 38 mm bore, verify shaft deflection against the needle length: these rollers tolerate little edge loading, and a simply supported span between 38 mm seats can bend past the compensation range long before the load rating is exhausted.
- 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.
- Contamination, not fatigue, kills most small needle bearings: with raceways this narrow, one hard particle dents a full-width line — seal the housing even when the bearing execution itself is open.
- The 25.5/49 kN ratings and 79 g mass are SKF catalogue values transcribed from ch. 7.3 of PUB BU/P1 17000 (PDF table page 630); combined-type axial ratings appear in the text above because the structured record carries radial values only.
Frequently asked questions
How is the NK 38/20 designation read?
NK names a machined-ring needle roller bearing without inner ring: the figures give Fw 38 mm and width 20 mm, OD 48 mm comes from the dimension series, and the flanged outer ring retains the caged rollers.
Can the NK 38/20 run on an unhardened shaft?
No. In this execution the 38 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.
How should the NK 38/20 be mounted?
Press on the ring faces only with a fitting sleeve, keep everything square to the 38 mm seat, and never transmit force through the rolling elements. Follow the catalogue's seat tolerances — the narrow needle contact forgives neither tilt nor burrs.
What limits the service life of a NK 38/20?
Beyond the L10 rating, the practical limits are journal/raceway hardness for the 38 mm seat, lubricant condition at the roller ends, and contamination through open ends — the 5.0 mm radial section leaves no reserve once a raceway is dented or ribboned.
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.