Threaded knob?

Hello, I have just received my WSME-200 ACDC TIG/MMA welder. There is a knob, on the front, in the lower middle, between the 7pin torch connector and the +connector. Unscrewing the knob reveals a threaded stud which appears to be for connecting a wire with an eye connector. Internally, the stud is not connected to anything. What is it for? The manual does not say, nor is it shown in the pics.

If your plasma torch has an extra single wire, connect that wire to this terminal. If not, you should not need it.