Clackers.. Two balls on a string you waved up and down, with a little ring in the middle. They were meant to bounce off each other top and bottom. Many a broken finger….
Made of hard plastic, some luminous green, other colours too. I remember them being quite heavy. The cord holding them together was made of nylon. The string was tied round the ring at the halfway point. You moved your arm up and down fast, the balls would be sent flying and bounce at the top and bottom of their arc, making the characteristic ‘clacking’ noise. Hence the name.
As with other toys from the 70’s I doubt they would have been approved by health and safety now!