The self-aligning ball bearing was invented by SKF. It has two rows of balls and a common sphered raceway in the outer ring.  The bearings are consequently self-aligning and insensitive to shaft deflections and angular misalignment of the shaft relative to the housing. Additionally, self-aligning ball bearings generate less friction than any other type of rolling bearing, which enables them to run cooler even at high speeds.
Self-aligning ball bearings are available with either a cylindrical or tapered bore. Bearings with a tapered bore can be mounted directly on a shaft or on an adapter or withdrawal sleeve.

SKF self-aligning ball bearings are available in several designs, including:
Open, basic design, bearings (fig 1)
Sealed, with contact seals on both sides (fig 2)
Open bearings with an extended inner ring (fig 3)