Import bearings require minimum work clearance, you must according to the condition selecting proper clearance. For example, gb 4604-93, rolling bearing radial clearance is divided into five groups - 2 group, 0 group, three groups, 4, 5 groups, clearance value, where 0 progressively larger group for standard clearance. Basic radial clearance group applicable to the general operation conditions, conventional temperature and the commonly used over surplus cooperation; In high temperature, high speed, low noise, low friction under special conditions such as work is appropriate chooses the bearing big radial clearance; For precise spindle, spindle use bearing appropriate chooses smaller radial clearance; For roller bearings can keep the amount of work clearance. In addition, for the bearing is indifferent separated type clearance; Finally, bearing installed after the clearance, work than before the installation of original clearance small, because bearing shall inherit certain load rotation, still need to import bearings cooperate and load generated by elastic deformation. Therefore, the import bearing radial clearance is not necessarily 55x55mm are.