Consists of 6 balls of six materials. Ideal for collision and pendulum expts. Perfect for pendulum experiments. It's a multi-purpose set ideal for pendulum experiments but can be used to meet a variety of lab. needs. Set includes 6 balls each 25 mm in diameter. Contains one ball each of wood, aluminium, steel, copper, brass and plastic. Each ball is drilled with 3 mm diameter hole. Supplied in plastic box.