The EquiKind+ bevel bit allows mild leverage with a lozenge to encourage a softer contact. The rings are larger on the 5" and 5.5" so the bit remains in proportion with larger horse heads. Mouthpiece thickness: 15mm. Cheek height: 55mm (4.5", 5"), 65mm (5.5"). The EquiKind+ coating is thinner than a rubber mouthpiece making them more comfortable for horses that don't have room for a thick mouthpiece and ideal for sensitive mouths or horses that don't like metal in their mouths. Stainless steel is used due to it being durable, easy to clean and resistance to rust.