There are two structures of self-aligning ball bearing, namely, self-aligning ball bearing with cylindrical bore and self-aligning ball bearing with tapered bore. The retainers are made of steel sheet or synthetic resins. Characterized by spherical outer ring raceway, it is self-aligning, and can compensate the error caused by different degrees of concentricity and axis deflection, but it shall not exceed 3 degrees relatively between inner ring and outer.  It can withstandheavier radial load, and also a certain amount of axial load at the same time. The outer ring raceway of this kind of bearing is spherical shape, so it has a self-aligning performance. The bearing can still work when the axle stands bending stress or leans and the relative tilt angle is less than 1 ~2.5 between the inner and outer ring center line.