Roller Bearings have inherently self-aligning function and also very strong.
Double row roller make the bearings can bear heavy load. Spherical Roller
Bearings have two rows of rollers and both use the same raceway in outer ring.
It also has two inner raceways.
Spherical Roller Bearings has self-aligning feature. This design makes bearings own the attractive design features and it can not be replaced in many demanding applications.