Like many people, I remain amazed by the sheer number of bit options out there. It can be an overwhelming subject to research, especially as a new horse person. As a person looking for a bit to fit a difficult horse, the cost of trying bit after bit to find the perfect comfort level for your horse can be daunting as well. Its easiest and best to be able to know the basic mechanics of bits you are looking at and then you can look at specific models that you think will work for you!
The first thing you need to know about bits is their basic anatomy. A bit is made up of a mouth piece, which is the part that goes through the mouth, and the cheek piece. The cheek piece is where the bit's connection points to the the bridle and the reins are. Cheek pieces come and many sizes and shapes, and have a variety of functions.
The next thing you need to know about bits is the terminology used when referring to certain kinds or parts! The two most basic terms you should to know are leverage and direct pressure, and the difference between the two. These terms split the bit world right down the middle and every bit falls within one of those halves.
Direct pressure bits are bits which attach to the rein and the bridle within the same ring on the cheek piece. Some examples of direct pressure cheek pieces, also called bit rings, are the O-ring, D-ring, Full Cheek and Eggbutt. These bits work off a 1:1 pressure ratio and are considered the most mild bits, especially for beginner riders and young horses. Direct pressure bits are most often seen in English disciplines and lower level Western disciplines.
Leverage bits are bits that connect to the bridle and rein via rings on opposite ends of a shank cheek piece. They are most often referred to as "shank" or "curb" bits. The anatomy of a leverage bit is more complicated than a direct pressure bit, because it has more parts
and works differently in its mechanics. The shank of a leverage bit has two parts, the portion of the shank above the mouth piece on which the bridle attaches called the purchase, and the portion bellow the mouth piece, called the shank or lever arm which attaches to the rein. These bits use leverage to apply a larger pressure to the horses mouth with a smaller force. The ratio of leverage applied is equivalent to the ratio in length between the purchase and the lever arm. So for example, a leverage bit with a 1 inch purchase, and a 2 inch shank will have a ratio of 1:2. In this case, for every pound of pressure applied to the rein, two pounds are felt by the horse. The trick to how a leverage bit works, is the curb strap/chain, which connects to the same rings as the bridle(on the purchase) and runs under the chin. When the rein is engaged, the curb strap stops the mouth piece and shank from rotating and thus enables the leverage effect to take place. When the curb strap tightens and the bit is engaged the rotation of the purchase also creates pole pressure encouraging the horse to lower its head and flex longitudinally. Leverage bits are most often seen in Western disciplines and in the higher levels of most English disciplines.
Once you have divided the world of bits into two halves by the terms direct pressure and leverage, you can then divide those halves even further, by what kind of mouth piece each bit possesses. There are hundreds of mouth piece options, and the easiest way to explain them is to explain the most common variations and the effect they have on how the bit works.
First we are going to talk about diameter of the mouth piece. A common misconception with newer horse owners is that a thinner bit is kinder because there is less of it. This can't be further from the truth. In reality, a smaller diameter is actually much harsher. To understand this better, think of a piece of 1/2 inch rope compared to a fishing line. If you loop the rope over the meat of your hand, and pull, you will feel pressure, but the pressure is spread over a larger surface so you won't really feel pain unless an extreme amount of force is placed on the other end of the loop. Now think of doing the same with the fishing line. It takes a much smaller amount of force to cause discomfort with using the line because the pressure is applied across a much smaller area. The diameter of a bit works the same way. A fatter mouth piece will spread the pressure out across the bars of the mouth more causing much less discomfort that a thinner one. So when choosing a bit, its best to use something with a good thickness to it.
Another area of mouth piece variation is the addition of joints to the bar. Bits come in many different jointed/non jointed configurations, the most common being solid, single jointed, and double jointed. These joints are generally seen in a link style or a ball joint style. Some mouth pieces are made with more than 2 joints, however they are generally more specialized in their application.
Single and double jointed bits are generally referred to as snaffle bits and are usually
used as a part of direct pressure bits. These mouth pieces allow the bit to have more flexibility which can be good for getting a softer mouth. However, when using a single jointed snaffle, you need to be very careful with how much pressure you use to accomplish your goals. A single jointed piece will collapse in the middle, as it is designed to do, which can cause the joint to close and raise upward, potentially poking the palate and pinching
the tongue in a "nutcracker" like fashion. This does not mean that the single joint snaffle is something that shouldn't be used but it does need to fit properly and be used carefully. A double joint greatly reduces the "nutcracker" effect by creating a gap with the middle piece in the bit. The are 3 main types of double joint bit(pictured bellow), the french link, the lozenge, and the ball joint. The french link is the least kind option because it has more defined edges that can be abrasive, where the ball joint offers the least break in the middle, eliminating the nutcracker effect while still offering flexibility. The lozenge type of joint offers a kinder more even texture for the horses tongue while retaining a looser feel.
A solid mouth piece has no joints and is usually made of metal, rubber, or a combination of the two. These bits are great for horses who prefer something more steady and stationary in their mouths where the jointed mouth pieces can come in a variety of styles to suit a horse who prefers a bit that moves and keeps them entertained. Solid mouth pieces are seen in direct pressure bits but are more common in leverage bits. When a solid mouth piece is in a leverage bit it will usually have a bend in the middle called a port. Ports come and many sizes and variations and allow a space for the tongue to rest comfortably under the bit. With a high ported bit, the port is also designed to touch the roof of the mouth if the bit is rotated past a certain angle.
Similarly there is a whole line of mouth pieces that are made of rubber and plastics
that are designed to get away from the cold rigid feel of metal and offer a more malleable and soft texture for the horse. These bits come in many varieties and are available in both leverage and direct pressure styles. These mouthpieces are most often used for horses who are very young or horses with super sensitive mouths as they are soft, flexible, and very forgiving.
Another common mouthpiece you will see is a twisted wire, or slow twist. These mouthpieces may not look too terrible but are very harsh, especially in inexperienced
hands. Thinking back to the above explanation of how thickness effects the harshness of pressure on the mouth, its not hard to see why these bits are extremely harsh. The wires twisted together make the illusion of a bit which is twice as thick, but the reality is that the pressure resting on the bars of the horses mouth is equivalent to the thickness of the one wire because the twist allows only one wire touch at any given time. This effect is also magnified by the abrasive texture of the twist. A slow twist is similar but instead of two pieces twisted together, it is a single, square shaped bar with hard edges that is then twisted to make the edges able to lay constantly against the bars of the mouth. I never recommend these mouth pieces to anyone because of the nature of how they are made to purposely produce discomfort. However, if you choose to use one, just know you need to have very quiet hands and it should be used on an experienced, finished horse.
Lastly there is a variety of bits which are inherently harsh and should not be used at all. This is because they have either conflicting mechanics or are made with pain in mind. Any piece of tack can be used in a way which inflicts pain, however there are some which do this anytime they are utilized.
One example of this kind of bit is an elevator or a "Gag" bit. This bit is designed to work in a leverage fashion, but with mouthpiece loose on a ring of the cheek piece. The reins and bridle are then attached to the main ring in a leverage system on opposite sides of the mouth piece ring. When the rein is engaged, the cheek piece rotates and applies pressure while also allowing the mouthpiece to move higher and higher in the mouth, stretching the lips, causing pain, and telling the horse to lift the head. When the mouth piece has reached its topmost position and can no longer travel along its cheek piece, the curb strap engages causing pole pressure which then tells the horse to put the head down. Thus this bit is not only extremely harsh with the lip stretch, but it also gives conflicting signals as to what the horse should be doing with its head. Other examples of nasty bits include bits made of things like bicycle chains, bits with sharp edges and corners, and bits intended to pinch the tongue and cause pain. These bits are usually used to cover up holes in a horses training by using pain and coercion to force the horse into submission.
Finally, when in doubt find someone experienced to help you! Bits have such a wide range of uses and benefits and it can take a while to find your perfect fit! If you struggle with the financial end of things, finding the right bit is especially hard because bits can average $50-$200 new. If you can't afford to buy new, there are lots of online sale sites, tack swaps, and consignment shops where you can buy bits used for a fraction of the price. While bits can be super confusing, its important to know the basics about them so that you are able to make the most educated decision you can for your horse.