Roller length (l) with a roller diameter (Dw) than the L/Dw>2.5 and roller diameter (Dw) called <6mm roller bearings needle roller bearings.
1. radial size of needle roller bearings is small, but very high radial loading capacity, unable to bear axial loads, use only as a free end bearing.
Facilitate device miniaturization and lightweight.
2. with or without the outer ring, the needle roller bearing without inner ring, only with a cage of needle roller components, requires matching the shaft or housing bore machining precision.
surface hardness should be identical to the bearing Raceway.
3. the needle bearing friction coefficient, not suitable for high speeds.