Straight and rigid Mullen Mouth bits exert steady and even pressure on the complete tongue. In comparison to jointed bits, a straight bar exerts less pressure on the tongue edges. The stronger the rein aid the more pressure is directed onto the tongue and lower jaw bone.

Recommended for horses that evade the rein aids and tend to get strong. In contrast to bridles with additional lever action on the poll (e.g. Pelham or Kimblewick), Mullen Mouth bits can be used for horses that dodge downwards and lean on the bit.