im pretty sure hes talking about the headtube, and how the folding rails rub against it since even a locked folding mech still usually has a little bit of play. usually putting a 3rd bolt keeps it pretty solid, ive ridden only 2 bolts for a long time now and it moves a bit but i ignore it. or you could always weld it and bolt it, that way it wont have any play at all haha