Needle bearing, also known as needle roller bearing, is a special type of cylindrical roller bearing. The rollers of this bearing are thin and long, which are called needle rollers. Although it has a small cross section, the needle roller bearing still has a high loading capacity. The cylindrical rollers of needle roller bearings have a diameter (D)≤5mm and value of length/diameter (L/D)≥2.5, the radial structure is compact. When the inner ring diameter and load capacity are the same as those of other bearings, its outer ring diameter is the smallest, which is especially suitable for supporting structures with limited radial installation dimensions.
Depending on the specific applications, a needle roller bearing without the inner ring or outer ring and even without the cage can be optional. In this case, the shaft surface and the housing hole surface that match the bearing are directly used as the inner and outer rolling surfaces of the bearing, like bearing rings. So the hardness, machining accuracy and surface quality of the shaft and housing hole should be similar to the raceway of the bearing ring. This type of bearing mainly supports radial loads. Needle roller bearings are widely used in machine tools, metallurgical machinery, textile machinery and printing machinery, which can make mechanical system designs very compact and flexible.