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 dimensions of needle roller bearings is small, but very high radial load capacity, unable to bear axial loads, use only as a free end bearing. Facilitate tool miniaturization and lightweight.
2. with or without the outer ring, the needle roller bearing without inner ring, only with a cage of needle roller parts, requires to match the shaft or housing bore machining precision, surface hardness should be identical to the bearing Raceway.
3. the needle roller bearing friction co-efficient, not suitable for high speeds.