(1) Self aligning ball bearing has two kinds of structures:cylindrical pore and tapered pore. Retainers are mainly made of steel sheet, synthetic resin,etc. Its feature is the outer ring raceway spherical surface and automatical adjusted, so it can compensate for the deviation caused by different axial angle. The relative gradient of inner and outer ring should not exceed 3 degree. (2) It can bear radial load and small axial load at the same time. The axial displacement is limited within the clearance limitation and it can adjusted automatically. It allows inner and outer ring work under the circumstances of relative tilt. It suits for bearing seat hole which can not be strictly to ensure concentricity components.