Two-Row Cylindrical Roller Radial Bearings: this kind of bearing can bear larger radial load and allow higher speed. The two rows of rollers in the bearing are arranged in a cross way. When rotating, the fluctuation frequency can be twice as high as that of a single row bearing, and the amplitude can be reduced by 70%. There are two types of commonly used bearings: NN30 / W33 and nn30k / W33. The inner ring of the two series of bearings has a stop edge, and the outer ring can be separated; nnu49 / W33 and nnu49k / W33 have a stop edge, and the inner ring can be separated. The inner rings of nn30k / W33 and nnu49k / W33 series are taper holes (taper 1:12), which are matched with the tapered Journal of the main shaft. Axial movement of the inner ring can make the inner ring swell, so as to reduce the shaft diameter Bearing clearance and even pre tighten the bearing. Cylindrical bore bearings are usually hot installed, and interference fit is used to reduce bearing clearance, or to achieve the purpose of preloading. For the nnu49 series bearings with separable inner ring, the main shaft is usually installed on the inner ring and then the raceway is finished to obtain high rotation accuracy of the main shaft