The string of beads is mainly used to count repeated mantras. So actually, it serves the same purpose as a rosary. Beads made of semi-precious stones, pearls, bodhi seeds, bone or wood may serve all kinds of goals, like counting any kind of mantras, or other forms of prayer, bows, walk-rounds and such. The cord is the same for every mala, and should be made of nine threads, symbolising the Buddha Vajradhara and the eight Bodhisattvas. The larger bead at the end stands for wisdom, realising the utter emptiness, and the cylindrical bead on top of the large bead symbolises the void itself. Together, they symbolise the triumph over all adversaries.