 This occurs when small vibrations form in the rotating shaft and become harmonically in sync with the speed of rotation, causing circular oscillations in the shaft.The oscillation causes the shaft to move in precession, and the timing of the rotation speed causes the balls or rollers to contact the races only when they are in similar positions.This forms wear marks caused by contact with the bearings and the races in specific areas, but not in others, leaving an uneven wear-pattern that resembles brinelling.