This bit works by putting pressure on the poll and the tongue. Attaching the reins to the lower rings will increase severity, it should be used with care. Mouthpiece thickness: 16mm. Cheek height: 135mm. 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.