The mullen mouth is very stable in the horseâ€™s mouth. It has a medium port creating space for the tongue and relieving pressure. Mouthpiece thickness: 12mm. Cheek height: 65mm. Blue sweet iron mouthpieces oxidise easily to create warmth with a sweet taste which helps with bit acceptance and encourages salivation. Please note the blue colour will fade with use. Stainless steel is used for the cheeks due to it being durable, easy to clean and resistance to rust.