The MB 04 is similar to the MB 02 in that it will rotate on the tongue
and apply tongue pressure, however, it has a small (¼") port that
introduces some tongue relief to the horse. The port allows the horse to
swallow and move his tongue when he is moving forward and relaxed,
which acts as a release or reward. The mouthpiece is curved, and it
wraps around the bars and lips instead of pinching.