Double-row ball slewing bearing has three seats . The steel balls bad the spacers may be directly arranged into the upper and lower raceways . Two rows of steel balls with different diameters are fitted according to the load . Such open mode fitting features ectraordinary convenience .The load angles of both upper and lower races are 90°. Which enable the bearing to bear large axial force and the overturing moment ,When the radial force is larger than 1/10 pf the axial force , the raceway should be especially designed ,The axial dimension and radial dimension  of double-row ball slewing bearing are rather large ,and the bearing construction is sturdy , hence it is especially suitable for tower cranes which requiring working diameter over medium range , mobile cranes and other unloading machines .