NKE K21X25X13 Nadelkränze (21x25x13)

As a needle roller bearing, this bearing carries high radial loads in a very compact section. The mounting dimensions are 21x25x13 mm and the weight is 0.01 kg; technical details beyond these are shown in the specification table. For confined mounting spaces under high radial load, the cage guides the needle rollers and holds them at pitch without a ring section taking up space.

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.