NK55-25-D-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-D-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 57 kN and C0 111 kN at the 55 mm seat; the C/C0 ratio of 0.51 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 19.7 kN, the limiting speed 8,400 r/min and the thermal reference speed 4,700 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 1.04 kN/mm and per millimetre of width 2.28 kN/mm — the reason 25 mm-wide needle bearings routinely replace much larger ball or roller positions mass is 195 g, just 0.11 g per mm² of projected 68×25 mm envelope, which keeps unbalanced forces low in fast-actuating linkages at 55 mm bore this is a mainstream industrial size — conveyor drives, winches and medium gearboxes use the 25 mm width as a standard mounting space NK55/25-D-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 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 X-life status (-XL) indicates the current Schaeffler premium execution at 55 mm bore; the 111 kN C0 rating reflects the improved rolling-contact geometry. The -D suffix supplies a radially split needle roller and cage assembly, so the cage can be fitted at bearing positions that cannot be reached over a shaft end. Typical applications include small electric motor accessory drives, rocker arms and valve trains and planetary gear bearings, where the 68 mm outside diameter and 57 kN dynamic rating match the duty. In small electric motor accessory drives the unit fits a compact 55 mm seat, and in rocker arms and valve trains the 195 g mass keeps unbalanced forces low in fast linkages. Designers also specify it for planetary gear bearings, relying on the 25 mm width and the published 111 kN static rating. Needle bearings are pure-radial units — any thrust must be taken by separate washers or an adjacent bearing, especially on flangeless RNAO/NAO. Without an inner ring the shaft is the raceway: 58–64 HRC and a ground, polished journal are mandatory, not recommendations.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• Needle bearings are pure-radial units — any thrust must be taken by separate washers or an adjacent bearing, especially on flangeless RNAO/NAO.
• Without an inner ring the shaft is the raceway: 58–64 HRC and a ground, polished journal are mandatory, not recommendations.
• 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.