Learn About the Action and Uses of a Tom Thumb Bit

How a Tom Thumb bit works

A Tom Thumb bit hanging on a green synthetic bridle.
K. Blocksdorf

A lot of riders think a Tom Thumb bit is a snaffle bit, and that it is a mild bit. But, it's jointed mouthpiece doesn't actually make it a snaffle, and it is a more severe bit than many people realize. In unskilled hands, it can be quite a harsh bit, and cause your horse to object and appear to misbehave. Here is what you need to know about this commonly used western curb bit.


Tom Thumbs have a jointed mouthpiece and medium length shanks from 5 to 7 inches long (15 to 18cm). The headstall of the bridle attaches to the rings at the top and a curb chain or strap attaches to the D-shaped slots. There are several types of mouthpieces found on Tom Thumb bits. These include various types of rubber and synthetics, rollers, and copper or copper inlaid strips. These bits have shanks, although shorter than many western bits, but nonetheless making it a leverage bit. The curb chain is a very important part of this (and all) curb bit, and should always be adjusted properly. A curb strap of leather or synthetic material might be used instead of a chain. This is to prevent the bit from rotating in the horse’s mouth too far.


Many people disagree on the severity of the Tom Thumb bit. Because it is jointed it has a nutcracker action in the mouth. Combined with the leverage action provided by the shanks the bit will apply pressure to the horse’s head over the poll, and under the chin as the curb chain or strap pulls upwards. If the reins are pulled hard, the joint in the mouthpiece bends and can come in contact with the roof of the horse’s mouth. This can cause the horse to toss its head—which is not safe.

How It Works

This bit is a curb or leverage bit. The rider’s signal is felt in the mouth, over the horse’s poll, and on the chin through the curb strap or chain. The Tom Thumb bit is often erroneously called a Tom Thumb snaffle. But the jointed mouthpiece does not make a Tom Thumb bit, which works on leverage, a snaffle bit. The leverage caused by the shanks make it a curb bit. 

The Tom Thumb is labeled as a bad bit by some, but like any bit, it depends on why it is being used, and the skill of the user. If it is being used to make your horse stop faster, you might consider why your horse isn’t stopping in the first place. Although a bit might make your horse stop faster in the short term, a horse will learn to ignore the bit, just as it has the previous bit it wore and will need another stronger bit down the road. Instead of amplifying the rein aids with a longer shanked curb bit, or another type of bit, it’s often better to school the horse and train the rider to have better skills.