You are looking at an original EARLY Lionel lock on that would fot O or 027. It can be used with ANY traditional O or 027 tubular style track. It cannot be used with roadbed style track such as Fastrack. It is much more heavy duty than the standard lock on that Lionel made in the postwar and modern eras.
It is just what you need to get power to the track from the wires coming from your transformer. This one is vintage, clean, and working.
CONDITION: C-7, Very clean. Shows use and light oxidation, but still quite usable.Pictures here are of actual item.