PURPOSE: To abolish the machining of a boss and a dust groove by providing a first process of preparing a socket and a plug, a second process of press-fitting the plug into the socket to form a dust groove, and a third process of caulking the end part of the small diameter cylindrical part of the plug to the end cover side and the socket side.

CONSTITUTION: In a first process, a socket 21 and a plug 28 are prepared. In a second process, the small diameter cylindrical part 30 of the plug 28 is press-fitted into the socket hole 24 of the socket 21 so as to form a dust groove 36 for mounting a dust cover between the step part 34 of the plug 28 and the head part 23 of the socket 21. In a third process, a bearing 37 and the ball part 39 of a ball stud 38 are enclosed in the enclosing hole 29 of the plug 28, with the ball part 39 fitted in the enveloped state to the bearing 37. After interposing an end cover 40, the end part 41 of the small diameter cylindrical part 30 of the plug 28 is caulked to the end cover 40 side and the socket 21 side. The machining of a boss and a dust groove can be thereby abolished.