Features: 1) Suitable for grooved axles or housing holes 2) Accuracy in high speed rotation will be kept when the geometric accuracy and hardness of the groove are specified 3) A kind of special rolling unit, the needles are guided by cage, shares small radical space but bears big radical load, especially useful when radical space is limited 4) Assemblies: single row and double row. The double row will bear bigger load, in special case, can be designed as separable needle and cage, easy to install and dismount 5) To achieve load capacity, the hardness of groove needs to be HRC58-640, hardness dept. to be 0.6 - 1mm, surface roughness Ra