NK38-20-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 NK38-20-XL model number is decoded

envelope 38×48×20 mm: 38 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 29 kN and C0 45 kN at the 38 mm seat; the C/C0 ratio of 0.64 is characteristic of a needle bearing — high static rating relative to dynamic in a compact 48 mm outside diameter the fatigue load limit Cur is 8.1 kN, the limiting speed 12,000 r/min and the thermal reference speed 7,200 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 0.76 kN/mm and per millimetre of width 1.45 kN/mm — the reason 20 mm-wide needle bearings routinely replace much larger ball or roller positions mass is 79.4 g, just 0.08 g per mm² of projected 48×20 mm envelope, which keeps unbalanced forces low in fast-actuating linkages 38 mm bore marks the medium range: mounting forces and fits become critical, and the 79.4 g mass calls for proper induction or press tooling rather than hand fitting Omitting the inner ring frees radial space — at a 38 mm shaft the outer diameter is only 48 mm and the width 20 mm, yet C is 29 kN The hardness requirement is unforgiving: below about 58 HRC the 38 mm journal brinels under the 45 kN static rating, and roughness above raceway finish accelerates roller wear 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 38×48×20 mm envelope. Typical applications include small electric motor accessory drives, rocker arms and valve trains and planetary gear bearings, where the 48 mm outside diameter and 29 kN dynamic rating match the duty. In small electric motor accessory drives the unit fits a compact 38 mm seat, and in rocker arms and valve trains the 79.4 g mass keeps unbalanced forces low in fast linkages. Designers also specify it for planetary gear bearings, relying on the 20 mm width and the published 45 kN static rating. 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. Needle bearings are pure-radial units — any thrust must be taken by separate washers or an adjacent bearing, especially on flangeless RNAO/NAO.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• 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.
• Needle bearings are pure-radial units — any thrust must be taken by separate washers or an adjacent bearing, especially on flangeless RNAO/NAO.
• On reciprocating duty ensure the stroke rotates the full needle set, or brinelling occurs at the same roller positions.