Needle roller bearings are roller bearings with cylindrical rollers that are both thin and long relative to their diameter. This type of roller is called a needle roller. Despite its smaller cross-section, the bearing still has a high load-bearing capacity. Needle roller bearings are equipped with thin and long rollers (roller diameter D≤5mm, L/D≥2.5, L is the roller length), so The radial structure is compact. When the inner diameter size and load capacity are the same as other types of bearings, the outer diameter is the smallest. It is especially suitable for support results with limited radial installation dimensions. Depending on the application, a bearing without an inner ring or a needle roller and cage assembly can be selected. At this time, the journal surface and shell hole surface matching the bearing are directly used as the inner and outer rolling surfaces of the bearing to ensure the load capacity and operating performance. As with ring bearings, the hardness, machining accuracy and surface quality of the shaft or housing hole raceway surface should be similar to the raceway of the bearing ring. This kind of bearing can only bear radial load.