Needle roller bearings (needle bearing) with cylindrical roller bearings, relative to its diameter, roller is fine and long. The roller called needle roller. Although it has a small section, the load bearing capacity of bearing still had high, with thin and long needle bearing roller (roller diameter of D = 5mm, L/D = 2.5, L as the roller length), so the radial structure is compact, the minimum outside diameter of the size of the inner diameter and load capacity and other types of bearings, especially for supporting the same, structure to the radial installation size restricted.