The outer ring of the selfcontained ball bearing in ground to a sphere, and the bore of housing in machined to a matching radius, This permits self-aligning between the two members. Following figure is a view of a Pillow Black which is the most popular type of Insert Ball Bearing Units with set screw locking. The bearing units have various types of perfect sealing devices and can operate satisfactorily under hard working conditions, especially for machines operated in dustry or muddy surroundings. Thus, they are widely used in agricultural machinery, construction machinery, textile machinery, food stuff machinery and conveying devices, etc.