Patent ID: 7585572

Claim:
A ball joint ( 2 ) comprising a ball stud ( 1 ) and a metallic socket ( 21 ), wherein: a ball stud ( 1 ) is made of steel and comprises a rod-shaped stud ( 12 ), a ball ( 11 ) is provided at one end of the rod-shaped stud ( 12 ), a metal plating film ( 4 ) is formed only on the surface of the stud ( 12 ); a trivalent chromate film ( 5 ) is continuously formed over both the surface of the metal plating film ( 4 ) formed only on the surface of the stud ( 12 ) and the surface of the non-plated ball ( 11 ), the metallic socket ( 21 ) is provided inside with a resin sheet ( 22 ) and the ball ( 11 ) of the ball stud ( 1 ) is fitted over with a resin sheet ( 22 ), and by forming the trivalent chromate film ( 5 ), generation of electrolytic corrosion at the boundary of the surface of the metal plated stud ( 12 ) and the surface of the non-plated ball ( 11 ) is prevented without preventing a smooth sliding motion between the ball ( 11 ) and the resin sheet ( 22 ).