Deep groove ball bearings are the most common type of rolling bearings. The basic deep groove ball bearing consists of an outer ring, an inner ring, a set of steel balls and a set of cages. There are two types of deep groove ball bearings, single row and double row. The deep groove ball structure is divided into two types: sealed and open. The open type means that the bearing does not have a sealed structure. The sealed deep groove ball is divided into dust-proof and oil-proof. seal. In general, the upper difference of the bearing inner and outer diameter tolerance is 0, and the lower difference is a negative value. For example, deep groove ball bearing 6206, the inner hole diameter is 30mm, the deviation is 0~-0.01mm; the outer diameter of the bearing is 62mm, the deviation is 0~-0.013mm. The specific bearing tolerances are determined in accordance with the standard according to the basic dimensions of the bearing's accuracy grade.