Needle roller bearings are equipped with thin and long rollers (the length of the roller is 3-10 times the diameter, and the diameter is generally not greater than 5mm), so the radial structure is compact, and its inner diameter and load capacity are the same as other types of bearings. The smallest diameter, especially suitable for supporting structures with restricted radial installation dimensions. Needle roller bearings can be used without inner ring bearings or needle roller and cage assemblies according to different applications. At this time, the journal surface and housing that match the bearing The surface of the hole is directly used as the inner and outer rolling surface of the bearing. In order to ensure the load capacity and running performance are the same as the bearing with ring, the hardness, machining accuracy and surface quality of the raceway surface of the shaft or housing hole should be the same as that of the bearing ring. Use combination rolling The needle bearing is a bearing unit composed of a radial needle roller bearing and a thrust bearing component. It has a compact structure and small volume, high rotation accuracy, and can bear a certain axial load while bearing a high radial load. And the product structure is diversified, adaptable and easy to install. Combined needle roller bearings are widely used in various mechanical equipment such as machine tools, metallurgical machinery, textile machinery and printing machinery, and can make the mechanical system design very compact and dexterous.