The port allows more room for the tongue, but will also apply pressure to the roof of the mouth. The slots in the D-rings allow for increased leverage on the poll. This bit should be used with care. Also known as a Uttoxeter Kimblewick. Mouthpiece thickness: 14mm. Cheek height: 100mm. Stainless steel is the most common material for bits. Durable, easy to clean, tasteless and does not rust.