Kimblewick Rubber Jointed Mouth Bit
Kimblewicks are similar to pelhams in their actions with the use of a curb but milder due to the lack of leverage a pelham shank would provide.
Kimblewick bit commonly used in general riding and provides more control on a horse that may be a strong puller or needs slight curb action to lower its head. It is quite common to see ponies wearing these bits.
With either type of Kimblewick, the curb chain or strap prevents the bit from rotating too far in the horse’s mouth. When the reins are pulled back, the bit applies pressure to the bars of the mouth, the chin and the poll. If there is a port, there may be pressure on the roof of the mouth. Because the bit has the equivalent of very short shanks, the curb action is relatively mild.
The single-jointed mouthpiece applies pressure to the tongue, lips, and bars. Due to the V-shape of the bit when the mouthpiece is contracted, it causes a "nutcracker" action, which has a pinching effect on the bars. It also causes the joint of the bit to push into the sensitive roof of the mouth if used harshly. A single-jointed bit with a curved mouthpiece has a more "U" shape tends to decrease the pressure on the roof of the mouth.
Rubber and hard plastics are used to encase a thin core of metal on some bits. These bits are generally thicker than many metal bits. Some horses might appreciate the softer feel of a rubber or plastic mouthpiece, while others may find them an uncomfortable mouthful. You might find older plastic or rubber mouthed bits give off a funny smell which your horse might or might not notice. Many plastic mouthed bits are made with a scent thought to encourage the horse to accept the bit more readily. This may encourage some horses to chew the bit and not carry the bit quietly. Both rubber and plastic mouthed bits do wear over time, sometimes quite quickly, leaving rough spots or exposing the metal core.