NK55-25-XL bearing: complete specifications & equivalents

Specification table

Source: catalog reference (HR1 2026-09-25) · extracted 2026-09-30

Parameters extracted from the official FAG Rolling Bearings catalogue (HR1 2026-09-25); FAG® is a trademark of Schaeffler Technologies AG & Co. KG, used here for identification only — mpnbase is not an authorized FAG/Schaeffler distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at schaeffler.com.

Cross references & equivalents

Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.

How the NK55-25-XL model number is decoded

envelope 55×68×25 mm: 55 mm seat is the hardened and ground shaft journal itself — there is no inner ring, with a thin 6.5 mm radial section packed with small-diameter needle rollers C is 45.5 kN and C0 82 kN at the 55 mm seat; the C/C0 ratio of 0.55 is characteristic of a needle bearing — high static rating relative to dynamic in a compact 68 mm outside diameter the fatigue load limit Cur is 14.3 kN, the limiting speed 8,400 r/min and the thermal reference speed 5,200 r/min; for small needle bearings the reference speed can exceed the kinematic limit, so the lower of the two governs the application dynamic capacity per millimetre of bore is 0.83 kN/mm and per millimetre of width 1.82 kN/mm — the reason 25 mm-wide needle bearings routinely replace much larger ball or roller positions mass is 180 g, just 0.11 g per mm² of projected 68×25 mm envelope, which keeps unbalanced forces low in fast-actuating linkages 55 mm bore marks the medium range: mounting forces and fits become critical, and the 180 g mass calls for proper induction or press tooling rather than hand fitting The hardness requirement is unforgiving: below about 58 HRC the 55 mm journal brinels under the 82 kN static rating, and roughness above raceway finish accelerates roller wear Reading the NK prefix: a machined (not drawn-cup) outer ring with the needle complement; an inner ring from the IR series can be added later if the shaft cannot be hardened The -XL suffix marks the X-life execution: refined raceway topography and upgraded materials lift the basic ratings versus the non-X-life bearing at the same 55×68×25 mm envelope. Typical applications include copying and printing machine mechanisms, gearbox selector and change linkages and hydraulic and pneumatic pump eccentrics, where the 68 mm outside diameter and 45.5 kN dynamic rating match the duty. In copying and printing machine mechanisms the unit fits a compact 55 mm seat, and in gearbox selector and change linkages the 180 g mass keeps unbalanced forces low in fast linkages. Designers also specify it for hydraulic and pneumatic pump eccentrics, relying on the 25 mm width and the published 82 kN static rating. On reciprocating duty ensure the stroke rotates the full needle set, or brinelling occurs at the same roller positions. Keep the specified radial clearance; an oversized shaft or heavy interference removes it and the needles bind hot immediately.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• On reciprocating duty ensure the stroke rotates the full needle set, or brinelling occurs at the same roller positions.
• Keep the specified radial clearance; an oversized shaft or heavy interference removes it and the needles bind hot immediately.
• Open ends draw contamination directly onto the needles; specify sealed or shielded positions in dusty environments rather than relying on grease alone.