Anti-friction bearing and a motor such a bearing

摘要

An anti-frictional bearing which is reduced in its asynchronous rotational run out so that the cumbersome analyzing operation of the raceway surface and selecting operation of inner and/or outer races are not required. The bearing will contribute for the high packaging density and high speed operation of the hard disk device. An anti-frictional bearing including an inner race way 1a formed on an outer peripheral surface of an inner race 1, an outer race way 2a formed on an inner peripheral surface of an outer race 2, and a plurality of rotating bodies 3 interposed between the race ways and retained by retainers 4 in a predetermined distance with each other, wherein an out of roundness of a raceway surface 1a, 2a of at least one of said inner and outer races 1, 2 is equal to or less than 0.05 mum.