NK42-20-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 NK42-20-XL model number is decoded

envelope 42×52×20 mm: 42 mm seat is the hardened and ground shaft journal itself — there is no inner ring, with a thin 5.0 mm radial section packed with small-diameter needle rollers C is 30 kN and C0 49 kN at the 42 mm seat; the C/C0 ratio of 0.61 is characteristic of a needle bearing — high static rating relative to dynamic in a compact 52 mm outside diameter the fatigue load limit Cur is 8.8 kN, the limiting speed 10,900 r/min and the thermal reference speed 6,600 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 0.71 kN/mm and per millimetre of width 1.50 kN/mm — the reason 20 mm-wide needle bearings routinely replace much larger ball or roller positions mass is 85.8 g, just 0.08 g per mm² of projected 52×20 mm envelope, which keeps unbalanced forces low in fast-actuating linkages 42 mm bore marks the medium range: mounting forces and fits become critical, and the 85.8 g mass calls for proper induction or press tooling rather than hand fitting This bearing accepts axial displacement between shaft and housing because the rollers rotate on the free journal; it locates nothing axially and must be flanked by guide faces The hardness requirement is unforgiving: below about 58 HRC the 42 mm journal brinels under the 49 kN static rating, and roughness above raceway finish accelerates roller wear As an X-life (-XL) bearing it benefits from the optimised surface finish that reduces friction and raises the fatigue strength behind the 8.8 kN Cur value. Typical applications include two-stroke and compressor piston pins, motorcycle and light-vehicle transmissions and rocker arms and valve trains, where the 52 mm outside diameter and 30 kN dynamic rating match the duty. In two-stroke and compressor piston pins the unit fits a compact 42 mm seat, and in motorcycle and light-vehicle transmissions the 85.8 g mass keeps unbalanced forces low in fast linkages. Designers also specify it for rocker arms and valve trains, relying on the 20 mm width and the published 49 kN static rating. On reciprocating duty ensure the stroke rotates the full needle set, or brinelling occurs at the same roller positions. Do not press an RNA/NK assembly in through the outer ring when mounting it on a shaft, and vice versa — rolling forces through the wrong ring bruises the raceways.

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.
• Do not press an RNA/NK assembly in through the outer ring when mounting it on a shaft, and vice versa — rolling forces through the wrong ring bruises the raceways.
• 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.