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"). Stainless steel is the most common material for bits. Durable, easy to clean, tasteless and does not rust.