A needle roller bearing is a special type of roller bearing which uses long, thin cylindrical rollers resembling needles. Ordinary roller bearings' rollers are only slightly longer than their diameter, but needle bearings typically have rollers that are at least four times longer than their diameter. Like all bearings, they are used to reduce the friction of a rotating surface.
Compared to ball bearings and ordinary roller bearings, needle bearings have a greater surface area in contact with the races, so they can support a greater load. They are also thinner, so they require less clearance between the axle and the surrounding structure.
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.
Needle roller bearings are a bearing that is classified as either radial or thrust depending on the direction of the load being supported. Needle roller bearings include bearings whose rollers slightly exceed the size range of needle rollers as stipulated by ISO. Needle roller bearings include drawn cup and solid radial bearings, as well as application-specific cam followers, and roller followers. Thrust bearings include thrust needle bearings.
Needle roller bearings are essentially cylindrical roller bearings except that their cylindrical rollers have a length 3 to 10 times their diameter (versus less a length less than 3 times their diameter). Therefore, the ratio of the bearing outside diameter to the inscribed circle diameter is small, and they have a rather high radial load capacity.
Even though they have a low cross section, precision needle roller bearings have a high radial load capacity and are exceptionally suited for bearing applications where radial space is limited.
