Mullen mouth bits are available in a large variety of shapes and materials. It is important to choose mullen mouth bits in the correct size for the horse as a bit that is too large can tilt and become uncomfortable for the horse when taking up the reins single-sided.   All rigid mullen mouth bits can descriptively be compared with a bicycle handlebar. The side of the mouthpiece where the rider gives a single-sided rein aid acts on the tongue, the opposite side moves forward towards the palate. Mullen mouth bits are commended to be used by skilled and experienced riders only as single-sided rein aids and the development of flexion and bent are impossible with rigid mullen mouth bits (bicycle handlebar). Riders who use a mullen mouth bit should therefore be able to rider the horse with weight and leg aids. A straight and rigid bar exerts steady and even pressure on the complete tongue (also the middle of the tongue).Compared to jointed bits less pressure is exerted on the tongue edges with straight bars. The stronger the reins are pulled the more pressure is directed onto the lower jaw bone via the tongue. Straight mullen mouth bits can be recommended for horses that evade the rein aids and get strong e.g. when approaching an obstacle. In contrast to bridles with additional lever action on the poll (e.g. Pelham or Kimblewick) mullen mouth bits can also be used for horses that dodge downwards and lean on the bit.   Mullen mouth bits with port Compared to straight mullen mouth bits no steady pressure is exerted onto the tongue with bits that have a port (e.g. KK Correction bit or CM mullen mouth).The middle of the tongue is more relieved with this bit shape and only squeezed with stronger rein aids. These bits are suitable for horses that resist the rider`s hand, have particularly fleshy tongues or for the correction of tongue vices of horses that perceive pressure on the tongue as uncomfortable and evade this pressure by pulling up or sticking out the tongue sideward. Flexible mullen mouth bits Compared to rigid mullen mouth bits the effect of single-sided rein aids is slightly better with flexible bits. Pressure is also distributed over the complete tongue when pulling the reins, but gets stronger towards the tongue edges. The “bicycle handlebar effect” described above is therefore a little bit weakend. Flexible mullen mouth bits (e.g. Flex Controlor Duo bit) can be recommended for horses that sometimes get strong or show unresponsiveness during the schooling of certain lessons or when approaching an obstacle. Flexible mullen mouth bits are often well accepted by horses that do not get along with jointed bits.