A thinner mouthpiece can make this bit a little stronger, however, it may be a more comfortable option for a horse with a small mouth. The smaller sizes of this bit come with smaller rings to ensure the bit remains in proportion. Mouthpiece thickness: 14mm (3.5″), 15mm (4″-4.75″), 17mm (6″). Cheek height: 55mm (3.5?, 4?, 4.5″), 75mm (5?, 5.5?, 5.75?, 6?).