23x26mm (7g) or 0.91x1.02in (0.247oz), recommended for all cats and dogs up to 10kg/20lb
26x31mm (9g) or 1.02x1.22in (0.317oz), recommended for dogs 10-25kg/20-50lb
32x36mm (12g) or 1.26x1.42in (0.423oz), recommended for dogs over 25kg/50lb
38x44mm (18g) or 1.49x1.73in (0.635oz), recommended for very large pets