NK47-20 bearing: complete specifications & equivalents
The NK47-20 is a DIN 616 radial bearing sized 47 x 57 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 | 47 mm |
| Outer diameter D | 57 mm |
| Width B | 20 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 29.2 kN |
| Basic static load rating C0 | 61 kN |
| Fatigue load limit Pu | 7.65 kN |
| Reference speed (thermal) | 8500 rpm |
| Limiting speed (mechanical) | 10000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 95 g |
| Manufacturer designation | NK 47/20 |
| 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 | 1.85 in |
|---|---|
| Outer diameter D | 2.244 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) | 31 of 46 |
| Bore above smallest NK-series size | 42 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NK47-20 model number is decoded
NK 47/20 belongs to the machined-ring needle roller family: an outer ring turned and ground to 57 mm with two retaining flanges, a roller-and-cage set inside, and envelope 47×57×20 mm on a hardened 47 mm shaft. Reading the designation: NK gives the series and the numbers the boundary plan — 47 mm Fw for the shaft seat, 20 mm width; the 57 mm OD comes from the dimension series, and the absence of an inner ring is built into the family name. 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. Selection arithmetic: C 29.2 kN against C0 61 kN gives a C0/C ratio of 2.09, and the 7.65 kN fatigue load limit Pu sets the floor for the adjusted-life calculation at contaminated lubrication. 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
- 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
- guide rollers running on hardened tracks
Known failure patterns
- needle edge loading and raceway denting when the shaft deflects beyond the compensation range
- polymer cage deformation when the local temperature exceeds the 120 °C sustained limit
- grease starvation at the roller ends when relubrication intervals are stretched in dirty duty
- hard-particle indentation in unfiltered lubricant
- smearing of rollers and journal during idle periods because the radial section holds too little lubricant
Selection pitfalls — read before you substitute
- At 47 mm bore, verify shaft deflection against the needle length: these rollers tolerate little edge loading, and a simply supported span between 47 mm seats can bend past the compensation range long before the load rating is exhausted.
- Reference and limiting speeds are different limits: the 8,500 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 47 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 29.2/61 kN ratings and 95 g mass are SKF catalogue values transcribed from ch. 7.3 of PUB BU/P1 17000 (PDF table page 632); combined-type axial ratings appear in the text above because the structured record carries radial values only.
Frequently asked questions
Does the NK 47/20 need a hardened and ground shaft?
No. In this execution the 47 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.
What mounting mistakes ruin a NK 47/20?
Press on the ring faces only with a fitting sleeve, keep everything square to the 47 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.
Is the NK 47/20 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 47/20 have?
A NK 47/20 measures 47 mm bore/Fw × 57 mm outside diameter × 20 mm width (1.85 × 2.244 × 0.787 in). From SKF catalogue PUB BU/P1 17000: radial dynamic rating C 29.2 kN, static C0 61 kN, fatigue limit Pu 7.65 kN, limiting speed 10,000 r/min, reference speed 8,500 r/min, mass about 95 g.
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.