The double-row Ball slewing bearing has three seat-rings. The steel balls and the spacers may be directly arranged into the upper and lower races. Two rows of steel balls with different diameters are fitted according to the force bom. 
Such open mode fitting features extraordinary convenience. The load angles of both upper and lower races are 90°, which enable the bearing to bear large axial force and the tipping moment. When the radial force is larger than 1/10 of the axial force the races should be newly designed. 
As the axle and the dimension of the double-row ball slewing bearing are rather large, the bearing construction is sturdy; hence it is particularly suitable for tower cranes which require working radius over medium range, mobile cranes and loading and unloading machines.