A needle roller bearing is a bearing which uses small cylindrical rollers.The difference of a needle roller bearing and roller bearing is the ratio of diameter and length of their rollers, when the ratio of the diameter and the length of roller of a roller bearing is between the interval of 0.4 to 0.1, that roller bearing is called as needle roller bearing. They are used to reduce friction of a rotating surface.
Needle bearings have a large surface area that is in contact with the bearing outer surfaces compared to ball bearings. Additionally there is less added clearance so they are much more compact. The typical structure consists of a needle cage which orients and contains the needle rollers, the needle rollers themselves, and an outer race
Needle bearings are heavily used in automobile components 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.