NK18-20-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 NK18-20-XL model number is decoded

envelope 18×26×20 mm: 18 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 17.9 kN and C0 22 kN at the 18 mm seat; the C/C0 ratio of 0.81 is characteristic of a needle bearing — high static rating relative to dynamic in a compact 26 mm outside diameter the fatigue load limit Cur is 3.9 kN, the limiting speed 22,100 r/min and the thermal reference speed 14,100 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 0.99 kN/mm and per millimetre of width 0.89 kN/mm — the reason 20 mm-wide needle bearings routinely replace much larger ball or roller positions mass is 31.4 g, just 0.06 g per mm² of projected 26×20 mm envelope, which keeps unbalanced forces low in fast-actuating linkages at 18 mm bore this size balances the 26 mm outside diameter against machineability of the adjacent parts — the most frequently specified band in the HR1 range NK18/20-XL has no inner ring: the needle rollers run directly on the shaft journal, so the seat must be hardened (58–64 HRC) and ground to bearing raceway quality The hardness requirement is unforgiving: below about 58 HRC the 18 mm journal brinels under the 22 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 3.9 kN Cur value. Typical applications include connecting-rod small ends, textile machine heald and cam shafts and motorcycle and light-vehicle transmissions, where the 26 mm outside diameter and 17.9 kN dynamic rating match the duty. In connecting-rod small ends the unit fits a compact 18 mm seat, and in textile machine heald and cam shafts the 31.4 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 22 kN static rating. Without an inner ring the shaft is the raceway: 58–64 HRC and a ground, polished journal are mandatory, not recommendations. On reciprocating duty ensure the stroke rotates the full needle set, or brinelling occurs at the same roller positions.

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.
• On reciprocating duty ensure the stroke rotates the full needle set, or brinelling occurs at the same roller positions.
• 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.