Patent ID: 7445387

Claim:
A ball bearing comprising: a ball supporting member having a hemispherical concave surface; primary small balls disposed so as to be movable in all directions on the hemispherical concave surface; a large ball disposed on the primary small balls so as to be rotatable in all directions; auxiliary small balls which are smaller than the primary small balls and are disposed so as to be movable in all directions on the hemispherical concave surface so as not to contact the large ball; and a casing having an aperture through which an upper portion of the large ball projects, and accommodating the ball supporting member, the primary small balls, the auxiliary small balls, and the large ball; wherein the primary small balls and the auxiliary small balls are disposed in the internal space surrounded by the large ball, the casing, and the hemispherical concave surface and the number of primary small balls and auxiliary small balls is selected so as to leave a gap at an upper part of the internal space that is at least as large as a primary small ball.