Patent ID: 8550741

Claim:
A ball joint comprising: a ball stud having a columnar stud portion and a ball portion that has a spherical side surface and a center positioned on an axis of the stud portion; a ball seat made of a resin and comprising a spherical concave bearing member having an inner concave bearing surface into which the ball portion is relatively rotatably and slidably fitted, and a substantially cylindrical holding member having an inner concave holding surface receiving a spherical outer circumferential portion of the concave bearing member; and a housing having a cylindrical cavity with a bottom surface having a through hole and holding the ball seat therein; the concave bearing member having an opening portion and comprising a plurality of circumferentially spaced resilient overhang members defining the concave inner bearing surface, the ball portion being inserted into the opening portion, the overhang members being integrally formed with the spherical outer circumferential portion of the concave bearing member and projecting toward a center of the opening portion, thereby resiliently withstanding a pullout load so as to prevent the ball portion from coming out therefrom; the holding member having an outwardly projecting thermal caulking member formed at a bottom portion of the holding member, the thermal caulking member being inserted through the through hole of the housing and thermally deformed, thereby fixing the ball seat to the housing; the concave bearing member being formed of a first resin material, and the holding member being formed of a second resin material, which has higher strength than that of the first material; and the holding member having a backup portion defining the inner concave holding surface and comprising a plurality of convex backup members which are formed by a plurality of slits extending in axial direction of the ball seat and arranged apart from each other in a circumferential direction of the holding member, wherein each convex backup member is closely adhered to an outer circumferential surface of a respective overhang member so as to cover and reinforce a portion of the overhang member.