All the ball bearings run on one principal that the load is transmitted from the outer race of the ball, and from the ball to the inner race. Several factors must be considered for choosing miniature ball bearings. To retain and prevent particular contamination from reaching critical surfaces seals and shields are used in these bearings, so great importance has to be paid while choosing a miniature component. For appropriate clearance the miniature ball bearing should include the compatibility of cage and shield type designs. The balls may be loosely restrained and separated by the means of a retainer or cage. For meeting the load, speed and temperature requirements of any application proper selection of bearing cage is very critical.