When is an inner ring required?

Whenever the shaft is not hardened and ground to the required hardness and surface finish. Needle rollers run directly on the shaft surface; a soft shaft will be indented within tens of operating hours.

What is the difference between HK and BK cups?

HK is open at both ends, BK has a closed end. BK is used at a shaft end where the bore also has to be closed off, saving a separate plug.

Needle roller bearings | e-Feniks

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Łożyska igiełkowe

Needle roller bearings offer the lowest section height relative to the radial load they carry — long, slim rollers give a large contact area with a minimal difference in diameters. They therefore work in gearboxes, clutches, pumps and mechanisms where every millimetre of radius counts.

The main designs are drawn cups (HK open ended, BK closed end), bearings with an inner ring (NKI, NA), needle roller cages running directly on a hardened shaft, and cam followers guided along a track.

What to look at when selecting

Without an inner ring the shaft becomes the raceway: hardened to 58–64 HRC and ground.
A drawn cup is cheap and compact but needs an accurate housing bore — its thin ring deforms when pressed in.
Check the mounting direction of the cup: the marked face takes the press tool.
For oscillating motion at low speed consider a plain bearing — needle bearings need motion to build a lubricant film.

Common questions

When is an inner ring required?: Whenever the shaft is not hardened and ground to the required hardness and surface finish. Needle rollers run directly on the shaft surface; a soft shaft will be indented within tens of operating hours.
What is the difference between HK and BK cups?: HK is open at both ends, BK has a closed end. BK is used at a shaft end where the bore also has to be closed off, saving a separate plug.