The roller bearing with the ratio of roller length (L) to roller diameter (DW) l / DW ＞ 2.5 and roller diameter (DW) ＜ 6mm is called needle roller bearing.

12.1 needle roller bearing has small radial dimension, but its radial bearing capacity is very high, so it can't bear axial load, so it is only used as free end support. It is conducive to miniaturization and lightweight of equipment.

12.2 when needle roller bearing without inner ring or outer ring is used, and only needle roller assembly with cage is used, machining accuracy and surface hardness of matching journal or bearing seat hole shall be the same as that of bearing ring raceway.

12.3 the friction coefficient of needle bearing is large, which is not suitable for high speed.