Similar to the MB 02, the MB 04 will rotate on the tongue and apply tongue pressure. However, it has a small (¼”) port that introduces some tongue relief to the horse. Acting as a release or reward, the port allows the horse to swallow and move his tongue when he is moving forward and relaxed. The mouthpiece is curved, and instead of pinching, it wraps around the bars and lips. It is available in two standard sizes, which are 5″ and 5.5″.