A ball joint or cap for an artificial hip joint is described that is suitable for carrying out a rotating or pivoting motion in an artificial hip joint socket, with a gap being provided for a natural fluid film (synovial fluid) between itself and the artificial hip joint socket, and with regular depressions without interconnecting channels between them being recessed in areas of its surface. It is proposed that its surface in the polar area is smooth and without depressions, that an area is provided in an intermediate area between the smooth polar area and its equator, in which depressions are recessed with hole widths between 1.0 mm to 3.0 mm, that adjacently in the intermediate area in the direction of its base edge, further depressions are recessed, the hole widths of which become steadily smaller, the closer they lie to the base edge, with hole widths between 0.5 mm and 1.0 mm.