Bicycle central shaft bearing 163110-2RS Inner diameter 16mm outer diameter 31mm thickness 10mm deep groove ball bearing 
Product grade: High-quality grade A (can replace imported bearings) and ordinary grade B (in line with national standards) 
Grade A: bearing inner and outer ring and steel ball are made of bearing steel, the hardness is HRA62 degrees, much higher than the hardness of ordinary bearings.  Add special grease for high strength bearing inside, the bearing has high precision of adaptation, good rotation flexibility, small friction torque, long service life (customers actually use more than 50,000 kilometers) professional supporting all kinds of high-grade bicycle axle.  (This type of bearing is customized for customers, in line with eu standards, long-term supporting export to Europe, America and Taiwan market) 
Ordinary GRADE B: the material, appearance, size and quality bearings are basically the same, but in the production and testing process can not reach the [quality grade] standard and degraded products, the bearing with precision, rotation flexibility and service life is poor, suitable for the general middle and low grade bicycles and garage maintenance department use.