Abstract: A signal plug structure includes a conductive bar, a conductive shaft and a sleeve. The conductive bar includes a reduced section thereof adapted to receive an elastic ring thereon. The elastic ring is made of a piece of thin metal being curved to an arcuate shape with cut-off sections thereon. Upon the conductive bar is inserted into a terminal, the elastic ring will be pressed by the inner wall of the terminal inwardly, thus the elastic ring produces an expansion force against the inner wall. This tightens the connection of the conductive bar and the terminal, and makes the conductive bar be able to fit any different size of terminal.