... hand in a stunning arc. Clackers, also known as click clacks, Knockers, Klackers, Bo-Los, Kerbangers, and ... make the pair of nearly 2" diameter balls clack (from opposite sides of a 12-18 inch ... - and that was part of the attraction) clack sound. If the sound of the balls clanging didn ... the Hula Hoop! The first (and probably only) Click-Clack world championships were held in Calcinatello, Italy in ...