There are many kinds of rolling bearings,models are complex,users should try to use the bearings that have standard dimensions program (don’t try to select a non-standard bearings). As the standard bearings are high-volume production, accuracy, quality, performance can be assured,the product cost is low. In order to limit the rolling bearing’s size, specification number, ISO15 International Standard specifies the dimension program of radial bearings; ISO104 International Standard specifies the dimension program of thrust bearings; ISO355 provides the dimension program of tapered roller bearings.