bw77

I have always adjusted the rear der using the adjuster located on the rd. I just noticed that there is another adjuster at the down tube cable stop, with a spring and knurling, but no threads that I could see. It turns with a pliers, but not by hand, even after I lubed it. When is the downtube adjuster used instead of the one on the rd? And should it turn by hand?

Thanks.

Bill