Self-tapping screw type fastener and push rod for brake booster using the same

A self-tapping screw type fastener of the present invention is characterized in that an external thread (7) of an adjusting rod (self-tapping screw) (5) is screwed into and fastened to an output rod (1) with tapping an internal thread (3) in an inner peripheral surface of a smooth prepared hole (2) of the output rod (1). The adjusting rod (5) has a threaded shaft (13) with the external thread (7) formed thereon and a smooth guide shaft (14) projecting from an end of the threaded shaft (13). The outer diameter (R1) of the smooth guide shaft (14) is set to be smaller than the major diameter (R4) of the external thread (7) and to be slightly larger than the minor diameter (R2) of the external thread (7) or the minor diameter (R3) of the internal thread (3). Because of the diameter difference "t" between the diameter (R1) and the diameter (R2) or (R3), a step (20) is formed so that the step comes in contact with the nearest ridge of the internal thread (3), thereby preventing the adjusting rod (5) from getting loose.