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.