Patent ID: 8142097

Claim:
A ball joint comprising: a ball stud having a stud portion at a middle thereof, a ball portion and a screw portion at opposite sides of the stud portion, a collar portion formed between the stud portion and the screw portion and having a larger diameter than that of the screw portion, wherein the stud portion, the ball portion, the screw portion, and the collar portion are formed integrally so as to form one piece of homogeneous construction, and a seat surface portion formed on a surface of the collar portion facing the screw portion; and a bearing member into which the ball portion is slidably fitted so as to universally pivotably-support the ball stud, wherein the stud portion is inserted through a mounting member, and a nut is screwed with the screw portion projected from the mounting member, and the seat surface portion directly abuts and is fastened to the mounting member by fastening the nut to the mounting member, the seat surface portion abutting the mounting member is directly formed with projections which prevents co-rotation of the ball stud when the nut is fastened and loosed, the projections have a height in a range of from 0.03 to 0.12 mm, thereby biting into the mounting member by an axial force caused by fastening the nut to the mounting member, and the screw portion has a stipulated value of screw torque in a range of from 40 to 60 N·m, wherein the projections are arranged along a circumference of the seat surface portion, and have a shape of trigonal pyramid in which a sharpened end thereof extends toward a center of the seat surface portion in plan view and side view.