Contact angle is the angle between a plane perpendicular to the
            bearing axis and a line joining the two contact points between the
            ball and the inner and outer raceways. The initial contact angle ao
            is defined as the contact angle when the bearing is subjected to a
            minimal axial load to remove the looseness resulting from radial
            play. The higher the radial play the higher ao. Further axial load
            will increase the contact angle see section on preload.