The fixed rings prevent pinching, whilst the brass alloy double joint distributes pressure over both the tongue and bars of the mouth to encourage mouthing and contact. Mouthpiece thickness: 13mm. Cheek height: 55mm (4.5", 5"), 75mm (5.5", 6"). Brass alloy mouth: Copper is alloyed with a harder metal to produce warm, durable mouthpieces which aid salivation. Stainless steel is used for the cheeks due to it being durable, easy to clean and resistance to rust.