Needle roller bearings are fitted with slender rollers. The roller length is 3 to 10 times its diameter, and the diameter is generally no more than 5 mm, resulting in a compact radial structure. While sharing the same bore size and load capacity as other bearing types, they feature the smallest outer diameter, making them ideal for support structures with limited radial installation space. The machining precision and surface finish of needle roller bearings shall be determined according to different operating conditions, bearing rings and service purposes. A needle roller bearing is a bearing unit composed of radial needle roller bearing and thrust bearing assemblies.