Rubber discs. For practice throwing discs. Size varies by weight. Size: 2.2 lbs (1 kg) = 7.1 inches (18 cm), 2.9 lbs (1.25 kg), 7.1 inches (18 cm), 3.3 lbs (1.5 kg), 3.9 lbs (20 cm), 3.9 lbs (1.75 kg), 4.5 inches (22 cm).