Shanked bit + Broken Piece = BAD BAD COMMUNICATION.
People think tom thumbs are nice because they are like a snaffle. On a true snaffle bit, the reins are attached to a relatively small, swiveling ring which could be considered a working part of the mouthpiece itself. When the rein is pulled, as you would do when asking the horse to turn, the ring that the rein is attached to moves completely away from the horse's mouth. The mouthpiece itself slides in the same direction, which causes the ring on the opposite side of the horse's mouth to apply pressure on that side. Because the horse is taught to go away from pressure, it then makes sense that if you are pulling to the left, and the pressure from the bit is on the right side of his mouth, he will naturally turn his head to the left. This is the simple principle that is commonly referred to as direct reining, or "plow reining". It is also a principle that is almost impossible to perform properly with the Tom Thumb, due to its design. Unlike a true snaffle bit, the Tom Thumb has shanks similar to the ones found on a solid curb bit. It is to the bottom of these shanks that the reins are attached. The headstall is attached to the top of the shank, as is some type of curb strap which fits around the bottom of the horse's jaw, in the chin area. These shanks swivel and are attached to the bit's mouthpiece.t is that one flaw in the bit's design that renders it almost totally useless when it comes to any kind of training which involves direct reining. Again, using direct reining in a snaffle bit, the horse is taught to move away from pressure. To turn to the right, the pressure is on the left side of the horse's mouth. To turn to the left, the pressure is on the right. There should be no other pressure being applied by the bit that could cause the horse to become confused.
Unfortunately, confusion is precisely what happens to a horse when the Tom Thumb is used. Because of its shanks, any attempt at direct reining results in pressure on several different areas around the horse's mouth. For instance, if you are aking the horse to turn to the left, you will be pulling on the left rein, with the idea that the pressure from the bit will be on the right side of the horse's mouth, thereby turning the horse left. However, because the rein is attached to the bottom of a swiveling shank, pulling on the rein results in the shank turning and tipping into the left side of the horse's face. When the shank tips, it also shifts the mouthpiece, which, in turn, puts pressure on the right side of the horse's mouth by pulling the right side of the bit into it. You now have pressure on both sides of the horse's mouth, as well as a shifting of the mouthpiece inside the mouth.
If this wasn't bad enough, tipping the shank also results in the tightening up of the curb strap that is under the horse's chin. Suddenly, the simple act of asking the horse to turn to the left is no longer a simple act. The bit is applying so much pressure in so many places, that the horse has no clue as to what you were asking for in the first place.
He then tries to tell you that he doesn't understand what you want by twisting his neck and shaking his head. Of course, we look at this as him being belligerent and not wanting to do what he was told. So, we simply apply more pressure to the rein which re****s in an even bigger fight on his part.
Eventually, the horse does finally turn to the left - but only as a last resort. Before he does, he will first try several different options. Among these will be: 1) turning to the right, because the left shank tipping into the side of his face is forcing him that way; 2) lifting his head as high as he can get it; 3) dropping his head as low as he can get it; 4) backing up. Rearing is also an option which sometimes happens as well.
Asking the horse to stop or back up, using a Tom Thumb, often results in much the same behavior. The reson for this is, again, the bit's design. Pulling back on the reins causes the hinged mouthpiece of the bit to collapse and jut foreward and then downward inside the horse's mouth, putting pressure on the horse's tongue. At the same time, the bottoms of the shanks (where the reins are attached) tip backward, causing the top of the shanks to tip forward. This, in turn, causes the curb strap to tighten under the horse's chin. Again, pressure is being applied in several different areas and this results in total confusion for the horse. Neck reining with the Tom Thumb can also result in confusion on the horse's part. This is because the idea behind neck reining is to be able to turn the horse by applying light pressure on his neck from the rein. To turn to the right, the rein is laid on the left side of the horse's neck. To turn to the left, the rein is on the right side of his neck. When done properly, there should be no movement or involvement whatsoever on the part of the bit. The solid curb bit, because of its design, lends itself very well to the act of neck reining. When laying the rein on the horse's neck to turn him, even if slightly heavy pressure is being applied, the curb bit usually will not move in the horse's mouth. This helps to eliminate the possibility of mixed signals which could confuse the horse.
However, because the Tom Thumb has so many moving parts, even the lightest pressure during neck reining with it often results in the shifting of the bit. Again, the shanks tip and turn causing the curb strap to tighten, the mouthpiece to collapse and the horse to become confused. The horse usually responds by raising his head and tipping it to the outside, or in the opposite direction that you want him to turn. Our response is usually to grab the reins with both hands and direct rein the horse back in the direction we want him to go. Of course this begins the series of problems that I mentioned earlier, head shaking, head tossing, and almost total unresponsiveness to anything we ask the horse to do.
I could go on and pull out further use full tidbits but that should be enough.