K 45x53x21 needle roller bearing is a roller bearing with cylindrical rollers. Compared with its diameter, the rollers are both thin and long. This roller is called a needle roller. Although it has a small 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). Therefore, the radial structure is compact. When its inner diameter and load capacity are the same as those of other types of bearings, its outer diameter is small, especially suitable for supporting structures with limited radial installation size.