The peanut copper link in this bit provides a warm metal for the horse?s mouth and helps to encourage salivation. This is a great bit for schooling. Mouthpiece thickness: 13mm. Cheek height: 165mm. Stainless steel is the most common material for bits. Durable, easy to clean, tasteless and does not rust. Copper is used in the mouthpiece, creating warmth and encouraging salivation to keep the mouth soft.