The little nut is a friction adjustment. The top pot metal nut is one of the big problems in that it can't be tightened enough to stay put. They conveniently rounded off the corners of the hex so the wrench slips, and if you try vise grips, they bind the thread so it can't be tightened, either. My final fix was to use blue loctite and then tighten it with a metric line wrench as much as possible. The mirror will then swivel under spring tension without coming unwound. I finally got disgusted and junked them.
10 Duc Streetfighter S (black)
67 Triumph Bonneville TT Special