Connection board is provided at one end of flexible board. In this way it is possible to test the dielectric capabilities of the electronic equipment in the laboratory and in situ and it is a simple matter to provide an electrical safety connection with conforms to a standard. The main portion also includes a shaft portion, a movable member having the engaging portion, and a cam mechanism disposed between the shaft portion and the movable member for allowing the shaft port ion to move separately from the movable member, so that the engaging portion engages the opening portion according to the vertical movement of the shaft portion through the cam mechanism. A knitting machine equipped with such a sinker is also described.