NK28-20 bearing: complete specifications & equivalents
The NK28-20 is a DIN 616 radial bearing sized 28 x 37 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 | 28 mm |
| Outer diameter D | 37 mm |
| Width B | 20 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 22 kN |
| Basic static load rating C0 | 36.5 kN |
| Fatigue load limit Pu | 4.55 kN |
| Reference speed (thermal) | 14000 rpm |
| Limiting speed (mechanical) | 16000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 52 g |
| Manufacturer designation | NK 28/20 |
| 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 | 1.102 in |
|---|---|
| Outer diameter D | 1.457 in |
| Width B | 0.787 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 4.5 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) | 20 of 46 |
| Bore above smallest NK-series size | 23 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NK28-20 model number is decoded
NK 28/20 is a machined-ring needle roller bearing without an inner ring: a solid outer ring with integral flanges guiding the caged rollers, riding directly on a 28 mm hardened shaft journal, as listed in SKF catalogue PUB BU/P1 17000. The NK 28/20 code states Fw 28 and width 20 mm directly; because the family has no inner ring, the 28 mm journal must be ground, hardened to 58–64 HRC and finished to the raceway tolerance the catalogue specifies. The machined ring is through-hardened and ground on OD, bore-side raceway and faces; the flanged lip design means the housing shoulder can be omitted — the ring clamps axially between housing wall and cover washer. Catalogue mass 52 g at 28×37×20 mm makes this one of the highest capacity-per-gram choices in the machined-ring needle roller bearings without inner ring; the limit is usually the shaft's ability to serve as a raceway, not the rolling contact itself. Grease through the housing groove before fitting the shaft; the integral flanges hold the grease film at the roller ends, which is where these bearings first starve.
Typical equipment & failure modes
Common applications
- cam followers built up from separate components
- crank pins and eccentrics where the hardened journal is the raceway
- gearbox planetary and idler gears on hardened pins
- piston-pin style pivots in hydraulic pumps
Known failure patterns
- raceway spalling once the catalogue L10 life is exceeded or after overload events
- polymer cage deformation when the local temperature exceeds the 120 °C sustained limit
- abrasive paste formation from dust ingressing past open ends without effective housing seals
- hard-particle indentation in unfiltered lubricant
- 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 28 mm bore, verify shaft deflection against the needle length: these rollers tolerate little edge loading, and a simply supported span between 28 mm seats can bend past the compensation range long before the load rating is exhausted.
- Do not interchange envelope-identical needle families blindly: NK 28/20 shares its 28×37×20 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 14,000 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.
- The 22/36.5 kN ratings and 52 g mass are SKF catalogue values transcribed from ch. 7.3 of PUB BU/P1 17000 (PDF table page 628); combined-type axial ratings appear in the text above because the structured record carries radial values only.
Frequently asked questions
What are the dimensions and ratings of the NK 28/20?
A NK 28/20 measures 28 mm bore/Fw × 37 mm outside diameter × 20 mm width (1.102 × 1.457 × 0.787 in). From SKF catalogue PUB BU/P1 17000: radial dynamic rating C 22 kN, static C0 36.5 kN, fatigue limit Pu 4.55 kN, limiting speed 16,000 r/min, reference speed 14,000 r/min, mass about 52 g.
How is the NK 28/20 designation read?
NK names a machined-ring needle roller bearing without inner ring: the figures give Fw 28 mm and width 20 mm, OD 37 mm comes from the dimension series, and the flanged outer ring retains the caged rollers.
Can the NK 28/20 run on an unhardened shaft?
No. In this execution the 28 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 28/20 be mounted?
Press on the ring faces only with a fitting sleeve, keep everything square to the 28 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.
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.