NK55-25 bearing: complete specifications & equivalents
The NK55-25 is a DIN 616 radial bearing sized 55 x 68 x 25 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 55 mm |
| Outer diameter D | 68 mm |
| Width B | 25 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 40.2 kN |
| Basic static load rating C0 | 88 kN |
| Fatigue load limit Pu | 10.8 kN |
| Reference speed (thermal) | 7500 rpm |
| Limiting speed (mechanical) | 8500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 180 g |
| Manufacturer designation | NK 55/25 |
| 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 | 2.165 in |
|---|---|
| Outer diameter D | 2.677 in |
| Width B | 0.984 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 6.5 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) | 33 of 46 |
| Bore above smallest NK-series size | 50 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NK55-25 model number is decoded
SKF's machined-ring needle roller bearings without inner ring include NK 55/25: 55 mm Fw, 68 mm outside diameter, 25 mm width — a machined and ground outer ring whose rolled flanges retain the needle rollers, running on the shaft as the inner raceway. The letters identify a flanged machined outer ring without inner ring; the figures give 55 mm Fw and 25 mm B — dimensionally identical envelopes exist with an inner ring under the NA/NKI names, which changes the shaft seat entirely. 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. Catalogue mass 180 g at 55×68×25 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. 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
- 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
- grease starvation at the roller ends when relubrication intervals are stretched in dirty duty
- corrosion pitting from condensation in intermittently operated machinery
- smearing of rollers and journal during idle periods because the radial section holds too little lubricant
Selection pitfalls — read before you substitute
- Above 50 mm bore, thermal growth matters: the 55 mm inner ring or journal grows with temperature faster than the housing, and the small clearance of a needle roller contact leaves little reserve — check running clearance hot, not just at assembly.
- 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 40.2/88 kN ratings and 180 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
How should the NK 55/25 be mounted?
Press on the ring faces only with a fitting sleeve, keep everything square to the 55 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 55/25?
Beyond the L10 rating, the practical limits are journal/raceway hardness for the 55 mm seat, lubricant condition at the roller ends, and contamination through open ends — the 6.5 mm radial section leaves no reserve once a raceway is dented or ribboned.
What are the dimensions and ratings of the NK 55/25?
A NK 55/25 measures 55 mm bore/Fw × 68 mm outside diameter × 25 mm width (2.165 × 2.677 × 0.984 in). From SKF catalogue PUB BU/P1 17000: radial dynamic rating C 40.2 kN, static C0 88 kN, fatigue limit Pu 10.8 kN, limiting speed 8,500 r/min, reference speed 7,500 r/min, mass about 180 g.
How is the NK 55/25 designation read?
NK names a machined-ring needle roller bearing without inner ring: the figures give Fw 55 mm and width 25 mm, OD 68 mm comes from the dimension series, and the flanged outer ring retains the caged rollers.
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.