NTN K21X25X17 Nadelkränze (21x25x17)

As a needle roller bearing, this bearing carries high radial loads in a very compact section. At 21x25x17 mm and a unit weight of 0.017 kg, the installation envelope is fixed; further technical details are held in the specification table. The needle roller and cage assembly consists of needle rollers and a cage without rings of its own; the shaft and the housing bore form the raceways directly.

The needle roller and cage assembly is a roller and cage set: it guides the needle rollers, holds them at even pitch and prevents them from rubbing against one another, but provides neither an inner nor an outer raceway. Both raceways come from the surrounding design, which is why the shaft and the housing bore must be hardened, ground and specified for rolling contact in roundness, roughness and case depth; where they are not, a version with rings of its own should be chosen instead.

Dispensing with rings gives the smallest radial section height while retaining high radial capacity, because the slender needle rollers carry over a long line of contact. The radial clearance of the bearing position follows from the dimensional chain of shaft diameter, bore diameter and rolling element diameter, and is therefore a result of the design rather than of the component.

Lubrication and sealing must be provided by the design; for the layout, raceway hardness, fits and the resulting radial clearance should be assessed together.