Anyone ever seen or used Tektro 872 canti brakes? There is an auction for them on the bay now:
The strange thing is that the return spring does not protrude out the base of the brake arm so that it can go through the little hole (or one of three holes, usually) next to the boss. Instead the base of the brake arm has two sections there is a spring between the two sections. But what keeps the base part of the arm from spinning on the boss? I suppose if the bolt as tightened down it would tend to hold it in place, but it hardly seems to be capable of holding it in place through many twists and torques of that arm.