Roller basic concept editing
Needle roller bearings are equipped with long, thin rollers (3 to 10 times the diameter of the rollers and generally no larger than 5 mm in diameter), so they have a compact radial structure and have the same internal diameter and load capacity as other types of bearings. The smallest diameter is particularly suitable for radial mounting dimensions with limited bearing results. According to different occasions, the inner ring bearing or needle roller and cage assembly can be used. The journal bearing surface and the housing hole surface matched with the bearing directly serve as the inner and outer rolling surfaces of the bearing to ensure load capacity and running performance. As with a bearing with a ring, the hardness of the raceway surface of the shaft or housing bore, the machining accuracy and the surface quality should be similar to the raceways of the bearing ring. This type of bearing can only withstand radial loads. 
1. Centripetal needle roller and cage assembly (K type);
2. Needle roller bearing with double locking ring in the outer ring (NA type, NKI type, RNA type, NK type);
3. Single row needle roller bearings with double ribs on the outer ring (NA type, NKI type, RNA type, NK type);
4. Double row needle roller bearings with double ribs on the outer ring (NA type, RNA type);
5, stamped outer ring needle roller bearings (HK type, BK type).
This type of bearing has low cost and large bearing capacity, and is suitable for the support structure with limited installation dimensions. The surface of the journal is hardened as the rolling surface, and the bearing is press-fitted into the seat hole without having to axially position it. Bearings should be filled with a proper amount of grease before installation. Normally, after assembly, BK type bearings are not needed for bearings with no protruding ends of the journals. The end faces are sealed and can withstand small axial travel forces.