Horse Tack Company stocks a huge number of English and Western Bits.
Measuring the mouth size, shanks and purchase is critical to both you and your horse. So lets identify the different parts first. The most widely used bit today is the snaffle bit. This bit is quit simple. Lets look at two examples. (1.) the Eggbutt snaffle. It is measured across the width of the snaffle mouth piece from ring to ring. (2.) The ring snaffle bit is measured the same way. However, the ring passes directly through the mouth piece. Thus is more prone to pinching. To prevent this some mouth pieces have an enlarged end which creates a barrier between the horses lip and the ring. Because of this you should measure from inside the radius to the opposite inside radius. Thus, if made correctly a 5 inch mouth piece will measure 5 ]1/4" from ring to ring.
Curb Bits which include Pelham bits, Kimberwick bits, Weymouth bits and most Western bits. Even shanked bits with a snaffle mouth are curb bits. To further clarify this. Any bit that employs a leather strap or chain under the jaw which exerts pressure to the jaw is a curb bit. Most of these bits are measured between the shanks. Pretty simple.
Bits range in size from 3 1/2" up to 7" in 1/4" increments. It is better to be a little bit than to be even a tad small. When placing a bit into a horses mouth be careful not to hit the horses teeth. This will cause your horse to become bit shy and make it more difficult to bridle the horse. The proper fit and adjustment of the bit is most essential, regardless of type. It should rest easily in the mouth, being sufficiently wide so as not to pinch the cheeks or cause wrinkles in the corner of the mouth. As a rule, curb-type bit rest lower in the mouth than a snaffle. All bits should be supplied with large rings, dees, or other devices to prevent them from passing through the mouth when either rein is drawn in turning.
Now, what you also need to know is how the different parts of curb bits work. I will start at the top of the the curb bit. This is the part that is above the mouth piece. It is called the purchase. The headstall cheek are attached here. Longer purchases apply more pressure to the poll area. Jimmy Williams a great California trainer used this concept to help young riders on the hunter circuit, back in the 60's and 70's. The shank which is below the bit can be short as on a Kimberwick bit or as long a 8 or 9 inches. The longer the shank the more pressure is applied to the bars and possible the tongue. The angle of the shank is also important. If the angle slants to to the rear the bit will produce a slower signal. If it is straight it will produce a quick signal. If the shank is mounted behind the mouth piece the bit will cause the horse to raise it's head and bring the hind quarters under the body. This is seen on the Walking Horse bit.
Curb Straps or Curb Chains
The curb strap or chain also plays a part in how your bit will signal your horse. The tighter the curb the faster the bit will signal. A tight curb strap can exert a great deal of pressure on the horses jaw and bars.
Severity of bits.
We have received comments about the severity of bits. We can only make this comment. In the trained hands of experienced riders most bits can and are used without causing undue distress on horses. However the mildest snaffle bit can cause pain if used incorrectly. Each rider has the responsibility to educate him or herself to the proper use of any bit. This is one of the ways we communicate with or horses. Poor communication gets poor results.