The fixed rings prevent pinching, whilst the sweet iron mouthpiece encourages salivation. Mouthpiece thickness: 14mm. Cheek height: 55mm (4.5", 5"), 75mm (5.5", 6"). Sweet iron mouthpieces are designed to oxidize to produce a sweet taste which helps with mouthing. Stainless steel is used for the cheeks due to it being durable, easy to clean and resistance to rust.