When you need to reduce friction between two moving parts but have very limited space to do so, a needle roller bearing may just be what you’re looking for. A needle roller bearing is a roller bearing with rollers whose length are at least four times their diameter. Despite their low cross section, the large surface area of the needle roller bearing allows them to support extremely high radial loads.
They usually consist of a cage which orients and contains the needle rollers and an outer race , which is sometimes the housing itself. The bearings can often be found in two different arrangements. The first is a radial arrangement, in which the rollers run parallel to the shaft. The second is a thrust arrangement, in which the rollers are placed flat in a radial pattern and run perpendicular to the shaft.
These bearings are often used in automotive applications such as rocker arm pivots, pumps, compressors and transmissions. The drive shaft of a rear-wheel drive vehicle typically has at least eight needle bearings (four in each U joint) and often more if it is particularly long, or operates on steep slopes.