| 摘要 |
When an outer diameter of an outer ring 4 is designated as D, an inner diameter of an inner ring 2 is designated as d, and a pitch circle diameter of respective balls 6 is designated as dm, a relationship of ((D+d)/2×0.85≦̸dm≦̸(D+d)/2×0.97 is satisfied. Further, when a diameter of the respective balls 6 is designated as Da, a axial width of a ball bearing is designated as B, a distance between centers of respective adjacent balls 6 in a circumferential direction is designated as L, and a sectional height of the ball bearing calculated by a relationship of H=(D−d)/2 is designated as H, all of relationships of 0.60≦̸Da/H≦̸0.75, and 0.58≦̸Da/B≦̸0.85, and 1.03Da≦̸L≦̸1.25Da are satisfied. Thereby, a structure capable of reducing rotational torque is realized without sacrificing durability.
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