NK25-20-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 NK25-20-XL model number is decoded

envelope 25×33×20 mm: 25 mm seat is the hardened and ground shaft journal itself — there is no inner ring, with a thin 4.0 mm radial section packed with small-diameter needle rollers C is 21.3 kN and C0 30.5 kN at the 25 mm seat; the C/C0 ratio of 0.70 is characteristic of a needle bearing — high static rating relative to dynamic in a compact 33 mm outside diameter the fatigue load limit Cur is 5.4 kN, the limiting speed 17,800 r/min and the thermal reference speed 10,400 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 0.85 kN/mm and per millimetre of width 1.06 kN/mm — the reason 20 mm-wide needle bearings routinely replace much larger ball or roller positions mass is 42 g, just 0.06 g per mm² of projected 33×20 mm envelope, which keeps unbalanced forces low in fast-actuating linkages with a 25 mm bore the 20 mm width and 21.3 kN C rating suit high-cycle industrial machinery rather than instrument duty The thin 4.0 mm section makes the 42 g bearing sensitive to seat geometry — a tapered or lobed journal preloads part of the needle set and shows up as local pitting 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 25×33×20 mm envelope. Typical applications include connecting-rod small ends, textile machine heald and cam shafts and motorcycle and light-vehicle transmissions, where the 33 mm outside diameter and 21.3 kN dynamic rating match the duty. In connecting-rod small ends the unit fits a compact 25 mm seat, and in textile machine heald and cam shafts the 42 g mass keeps unbalanced forces low in fast linkages. Designers also specify it for motorcycle and light-vehicle transmissions, relying on the 20 mm width and the published 30.5 kN static rating. Without an inner ring the shaft is the raceway: 58–64 HRC and a ground, polished journal are mandatory, not recommendations. Adding an IR inner ring changes the envelope logic: the same outer assembly then fits a smaller shaft — recheck bore, clearance and ratings when substituting.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• Without an inner ring the shaft is the raceway: 58–64 HRC and a ground, polished journal are mandatory, not recommendations.
• Adding an IR inner ring changes the envelope logic: the same outer assembly then fits a smaller shaft — recheck bore, clearance and ratings when substituting.
• Keep the specified radial clearance; an oversized shaft or heavy interference removes it and the needles bind hot immediately.