Self-aligning ball bearing has two-two balls and one concave outer raceway. This bearing is self-aligning accordingly and can resist the misalignment of shaft with bearing box. This bearing is mainly used for carrying radial load and samll axial laod, but can not carry axial load if without radial load. This bearing is used especially for the applications with serious shaft deflection or misalignment so it is widely used in machinery industry such as precision meter, low noise electric motor, excise equipments and other general machinery.