In the past, on every horse forum I've joined, I've posted a reference guide to bits and bitting listing materials, types, and usage for common equipment. People seem to appreciate the resource, though I always find it underutilized (the plethora of redundant "What's the best bit for starting colts?" and "What does a Tom Thumb do?" threads are evidence of that). Oh well.
However, I see that this forum already has two such bitting guides. They seem to be pretty complete and accurate, which is great. There are a few things I would quibble and disagree with, but I suppose that is to be expected. Rather than derail those pre-established threads, though, I thought I'd just post my own overview here...for questioning, for debate, for education...whatever.
INTRODUCTION There are literally hundreds of types of bits on the market, and the options can be overwhelming for someone looking to make a selection for his or her horse. From the most basic $5 curb to several hundred dollar custom bits and the "fix-all" fads, the variety is astounding.
While a solid foundation is of the utmost importance and no bit can fix training issues on its own, it is true that each bit works in a different way and serves a different purpose. Some horses work better in one type of bit, while another might prefer something entirely different. It's up to the trainer to find something that the horse works well in to reach the animal's full potential.
As a horse matures, grows, and changes, its bitting needs will probably change as well. If it begins to have training "issues," it may be time to step back to basics with a gentler bit, not reach for something harsher with more control. This guide is intended as a basic overview and resource for the selection of material, mouthpiece, cheek, and construction in the choice of bitting for a Western or English horse in training for any discipline. Always consult a trainer if unsure of the bit that works best with your riding ability and your horse's conformation and experience level. Some horses, due to varying heights of palate, tongue injuries, or other issue, will not be able to accomodate some mouthpieces, or may do best with a non-bitted alternative. Also, never forget the importance of good veterinary and dental care in the response of a horse to any tack choice. _______________________________________ Materials:
Plated metal bits are almost exclusively low end in terms of quality and price. While they may initially be aesthetically pleasing, regular use will cause the plating to chip off, creating a sharp/rough edge to cut and irritate the tongue and bars.
Stainless steel is probably one of the more common materials on the market (especially in cheaper bits, though this does not mean it's neccessarily a bad thing). It tends to dry the mouth out more than some other metals, but some horses simply seem to prefer it to the alternatives. It is very durable, easy to clean, and will not rust--so it looks good and lasts virtually forever.
Another common material, sweet iron increases salivation and encourages horses to play with and accept the bit. Many horses like it for this reason. Because it rusts and turns dark, it doesn't look as "pretty," but it does tend to last a long time if cared for.
Copper also encourages salivation. It can be found either in the entire mouthpiece (rather uncommon) or as inserts in either a stainless or sweet iron bit (very common). This is a softer metal, so completely copper bits may not last as long as others, especially if the horse chews on it due to its taste. Some horses will not tolerate the taste.
A rubber (or rubber coated) mouthpiece is very gentle. A completely rubber mouthpiece will bend with the mouth when a lot of pressure is applied. Some horses love these bits; others absolutely despise them and will run through them. If your horse tends to chew on or mouth the bit, the mouthpiece will have to be replaced periodically as they will literally bite through the rubber. Some rubber bits are flavored like apple or peppermint and are used to introduce a young horse to a bit or teach a horse to take the bit.
Plastic is a less common material for bit construction, but made popular by the English "Happy Mouth" series. It is fairly delicate (but holds up well when horses don't chew the bit) and gentle (like rubber, though far less flexible). As an active-mouthed horse chews on the mouthpiece, it may become rough and sharp, and for this reason, plastic has a very mixed review among horse trainers. In addition, the fatness of a plastic mouthpiece may not accomodate a horse with a low palate.
Aluminum is used fairly frequently on the shanks of bits, but is not as common in mouthpieces due to some controversy as to whether or not it's toxic. Aluminum is said to dry out the mouth. Its main advantage is that it is lightweight, unlike the other materials, but this is a matter of personal preference. It's very soft and can get chewed up easily. Aluminum mouthpieces are most commonly seen on gaited horse bits. __________________________________________________ ___-
Why this mouthpiece is called a "snaffle" is a mystery to me, as snaffle actually refers to an unshanked bit. Still, tack catalogs and trainers alike often refer, incorrectly, to a "snaffle mouth." Regardless, this is a very widespread mouthpiece--perhaps the most common of all. When you pull back on the reins, pressure is applied to the bars of the mouth. It also pulls back on the tongue. Depending on the construction of the bit, the middle joint may hinge inwards in the "nutcracker effect." This may cause a pinching of the tongue, and in extreme cases, the point may reach the roof of the mouth, but contrary to popular opinion, this is extremely rare and results from a very poorly made bit or a usage of the reins far outside of their normal scope. In reality, pulling back increases tongue pressure and decreases palate pressure 99.9% of the time. Despite this, the snaffle mouthpiece is considered pretty mild and can be found with many different styles of shanks. It's especially popular for starting bits.
This mouthpiece is often rounded, smooth, and of medium diameter. In general, the thinner and rougher the mouthpiece, the harsher the bit.
Other varieties include the twisted wire, whose texture works on the bars and tongue with more sensitivity:
The extra-thin wire (extremely harsh; can cut the mouth):
The double wire, whose twin mouthpieces create a "scissor" effect in the mouth, pinching the tongue:
Several squared off, rubber, or extra-wide varieties also exist on the market.
The single-joint is a good mouthpiece for general riding, breaking, training, and fixing vices, although its exact use depends on the shanks it's mounted on.
The three-piece mouthpiece is similar to the single-joint mouth in that it works off bar pressure and provides only limited tongue relief. When pressure is applied, the two outside pieces pull into the bars and flex at the joints. The center piece stays flat and lies against the tongue. This is in contrast to the two-piece snaffle mouth, which collapses and shoots upwards in the “nutcracker effect.” For this reason, the three-piece is much less likely to pinch and is considered milder, although it has the same amount of control.
Variations include the dogbone:
The roller (which gives an anxious horse something to play with):
And the lifesaver (pinching is virtually impossible, but the center ring will pull tight across the tongue, and can roll into the tongue quite severely):
Because it is simple and gentle, the three-piece mouth is also a good starting, breaking, and problem-fixing mouthpiece—once again depending on the shanks it is mounted on. Many horses prefer a three-piece mouth over a two-piece one.
In the English world, three-piece bits are usually called either French Link or Dr. Bristol, the difference being how the middle joint folds. A French link folds gently over the tongue and lays flat and does not press into the palate, whereas a Dr. Bristol's middle link is turned sideways--and often squared off--so that the link does press into the palate and tongue.
The “port” is the little thingy in the center of the mouthpiece that curves upwards toward the roof of the mouth. It may be solid, but is usually open underneath—which provides tongue relief for a broke horse. Generally speaking, the wider the port, the more tongue relief and the milder the bit; the taller the port, the more likely it is to come in contact with the roof of the mouth, which can be severe, although many seasoned horses work off this type of pressure.
A moderate port is often called a “correction mouthpiece” and is found almost exclusively on shanked bits, with a few exceptions.
A narrow port, such as the one above, provides little to no tongue relief. The attachments at the joints allow for folding motion only in one action; thus, the bit can collapse onto the bars, but the port cannot be lifted off of the tongue. A solid, unbroken ported bit works well on broke horses who know how to neck rein, as it gives them tongue relief and does not interfere with many moving parts. However, most three-piece ported bits do not move in the expected three-piece manner because they are hinged vertically, not horizontally, and do not respond to independent shank movement.
Compare that to this bit below, which allows for horizontal swiveling and increased independence of rein commands:
A cathedral bit has a very high, narrow port and is best left for very broke horses and experienced trainers who understand the bit's action.
A low, wide, broad port, on the other hand, provides a lot of tongue relief, although on a solid mouthpiece, it does not allow for much independent side reining.
The chain is considered a harsh mouthpiece because it conforms to the horse’s mouth and does not give any tongue relief whatsoever. It can also pinch, and rough hands can grate the chain across the lips, potentially cutting them. On the other hand, the fact that a chain conforms to the mouth can make it very comfortable for a horse to carry when the reins are loose. Chain mouthpieces are often found on gag shanks or solid shanks and are very popular with gaited horses and in the world of rodeo, particularly for ropers and barrel racers. In the right hands, a chain mouthpiece can teach lateral movement and flexion as well as getting a good “whoa.” In the wrong hands (or in the wrong mouth) it can be disastrous.
A variation is the bikechain or “mule bit” mouthpiece. It is usually sawed/serrated on one side, and smooth on the other and reversible for different effects. While I won’t condemn any bit entirely and say it should never be used, I can’t imagine any instance where a rider would need something this harsh and dangerous. It can certainly pinch and cut.
The fat mouthpiece bends and folds with the horse. The balls press into nerves on the horse's tongue that are not generally affected with other mouthpices. Some horses love this bit; others hate it.
The Mullen mouthpiece is smooth, thick, and solid. It may be flat (lots of tongue pressure) or slightly curved (some tongue relief). It is often found on short, solid shanks and advertised as a “colt bit.” It is not harsh at all, but it has very little finesse, so teaching things like collection and lateral movement are extremely difficult. The Mullen mouth is good for teaching “whoa” and getting a young horse used to a shanked bit without scaring him, or as an alternative to the pinching of a snaffle mouthpiece. It may also work on older, broke horses who don’t respond well to other mouthpieces and need tongue pressure. Rubber or plastic mouthpiece are often Mullen in design.
The simplest type of bit, the characteristics of a snaffle are no shanks, no leverage action, and no curb. They work directly off of rein pressure--the same amount of pressure is applied to the mouth as is applied by the hands. Snaffles are often used as beginning bits to introduce a horse to having something in its mouth and respond to different sorts of rein contact. They are generally pretty mild (depending on the mouthpiece). In Western disciplines, snaffles are often used with a curb strap or bit hobble that serves no purpose other than to position the bit correctly and keep it from pulling through the mouth.
The different cheek pieces include O-ring/loose-ring (when you pull right, the right side of the bit tightens against the bars and the bit may pull through the mouth; the mouthpiece is free to rotate around the circumference, and pinching may occur at the mouthpiece connection):
D-ring (the mouthpiece is fixed in place; when you pull right, the right side of the bit tightens against the cheek and the outer left side of the bit pulls into the left side off the mouth--this allows for outside "pushing" as well as inside "pulling" cues):
Eggbutt (pretty similar to a D-ring, a little less opposite side pressure and slightly more likely to pull through the mouth):
Half Cheek (applies lots of pressure on the opposite side):
Full Cheek (applies tons of pressure from the opposite side on both top and bottom, giving horses a "push in the right direction"--this is why it can be a good bit for young or stiff horses; also, the vertical cheek pieces are often controlled with keepers in the bridle):
Curb bits are not for young, green, or inexperienced horses due to their often-indirect and advanced action; rather, horses must be transitioned into them gradually as broke-ness, finesse, and responsiveness increase. Curb bits differ from snaffles in that they apply leverage pressure in the form of a curb strap or chain. The shanks increase the amount of pressure that is applied to the mouth, magnifying the hands’ action. When the reins are pulled, the bit rotates in the mouth. The mouthpiece engages more fully as more pressure is applied, the curb tightens, and when it has tightened as far as it can go, strong pressure is applied to the mouth. Curb bits will also apply some degree of poll pressure, though for most this is very minimal. Generally speaking, the longer and straighter the shank, the more the pressure is magnified, and the harsher the bit. A long purchase (the upper part of the shank between the mouthpiece and bit hanger) also increases leverage and severity. A long, curved shank bit gives some warning in between the time the reins are picked up and the bit engages, while a short, straight shank bit engages almost immediately. Mild curb bits are great for teaching collection, flexion, and lateral movement. A short, curved-shank curb with a three-piece or snaffle mouthpiece is good for introducing a young horse to leverage pressure without scaring him after he has graduated from a snaffle. A curb with a solid or correctional mouthpiece is considered “the” bit for broke Western horses who know how to neck-rein—there is no direct reining here, as the fixed shanks do not allow for independent side movement.
In terms of curb construction, the mildest is flat leather, followed by rawhide, double chain, single chain, and finally the severe “power curb.” A tighter curb means the mouthpiece will engage sooner.
Gag bits (called elevator bits in the English world) seem to have a negative connotation, perhaps because their name conjures up images of a horse spitting and choking on a too-tight mouthpiece. In fact, when used correctly, gag bits can be quite mild. I personally like them (and Wonder/Half-Wonder bits in particular) for teaching collection, flexion, and lateral movement to a green horse moving out of a snaffle. Gag bits are popular in the training pen, barrel racing and in gaited horse communities.
Physically, they are composed of the mouthpiece (often a chain or snaffle mouth), shanks of varying lengths, and a curb. What sets them apart from ordinary curb bits is that the mouthpiece is not fixed in place—it is free to move and slide about. This is the “gag action.” When pressure is applied via the reins, the bit rotates and the mouthpiece slides around the ring. When the curb has tightened as much as it can and/or the mouthpiece reaches the end of its track, increasing pressure is applied from the mouthpiece. Poll pressure is also applied as the curb mouthpiece slides and the bridle effectively shortens. This gag action gives the horse plenty of warning from the time the rider picks up the reins to the time harsh pressure is applied. It also allows for independent movement of the shanks, meaning you can “pick up” one side of the horses head without affecting the other—great for lateral movement.
English elevator bits are often used without a curb, making them similar to draw bits, which will be discussed later.
Draw bits consist of an unshanked bit with two rings through which a rope, cable, or curved piece of metal is run. The reins are attached to the end of this. A piece of leather, rope, cable, or wire (in order of increasing severity) is run behind the ears and attached to the cord running through the bit. When the reins are pulled back, the cord is also pulled, tightening the rope behind the ears (poll pressure) and lifting the bit. The bit slides along the cord until it can go no further. The bridle shortens, and increasing mouthpiece pressure is applied.
If the draw bit also has gag action and a soft ope is run behind the ears, this is a very mild bit and good transition from a snaffle, especially for teaching lateral movement. If the bit is more snaffle-like, has a harsh mouthpiece, or a cable or wire is run behind the ears, this bit can become quite severe. Draw bits work well on soft-mouthed horses, young horses, or those who don’t respond well to curb or noseband pressure.
Combination bits (sometimes called bitted hackamores) consist of a curb bit (almost always a gag bit) and a noseband made of leather, chain in tubing, rope, rawhide, bike chain, or twisted metal (in order of severity). They work best on seasoned horses who already know their jobs and do well with a little guidance, but do need some help steering and stopping. There’s a lot of action and a lot of different moving parts in a combo bit, so it can scare off a young or inexperienced horse.
When pressure is applied, the action is the same as that of a curb or gag bit, but additional pressure comes from the noseband, which presses down on the face. Adjusted too low, the noseband can damage the nasal bones, but adjusted properly it encourages the horse to rate or sometimes drop its head. Most combo bits aren’t incredibly harsh, because the pressure is distributed across so many different places. However, those with severe nosebands, harsh mouthpieces, or long shanks can be quite brutal. Most horses don’t need all the extra action and control provided by these bits and will only be confused by all the stuff going on. Most combo bits should only be used by skilled, experienced riders on very well trained, broke horses.
Lifter bits combine a tiny amount of gag action with a long purchase. They’re fairly harsh, particularly when combined with a severe mouthpiece, and are used for encouraging a broke horse to “lift” his nose—lateral movement. Lifter bits are popular with barrel racers who need to get their horse’s nose quickly during a run.
A sidepull is often used as breaking equipment for a young horse, as it is extremely gentle. It works entirely off of direct rein movement, although a very soft-mouthed broke horse who knows how to neck rein would work fine in it, as well. A sidepull consists of two rings (to which the reins attach), a noseband, and a piece that loops underneath the jaw and holds everything in place. Rein pressure applied to one side pulls against the opposite side—hence the name. When the reins are pulled straight back, the noseband and underneath "curb" piece apply light pressure. Collection, flexion, and lateral movement are difficult to achieve due to the mildness and simple action. Getting a good “whoa” may also be hard. Sidepulls are generally constructed of rope or rawhide, although chain and cable varieties exist and negate the mild effect. Sidepulls are sometimes combined with snaffle bits.
The word “hackamore” in modern usage most commonly refers to a piece of equipment consisting of a noseband, varying styles of shanks, and a curb chain. When the reins are pulled back, the noseband puts pressure downward on the nose, the shanks rotate back, and the curb chain is tightened. Once again, longer and straighter shanks usually correspond to a harsher effect, and the construction of nosebands is the same as with the combination bit. Hackamores work well on horses who despise bits or need noseband pressure but not a full combo bit. Depending on the style, the hackamore may be very light or very harsh. It can have a lot of finesse and lateral control, or it can have none whatsoever—all hinging on the shank design. Most hackamores have quite a bit of “whoa” and most don’t have quite as much “pick up” or turn. Due to their severity in some cases, hackamores can be downright dangerous or abusive in unskilled hands who don't understand how to communicate cues appropriately with this equipment.
The original hackamores were made up of a noseband, called a bosal, a headstall part, called a hanger, sometimes, a piece that ties under the chin to help keep the hanger on, called a fiador, and a one piece long rein to be tied, called a mecate. There are no metal or shanks on this piece of equipment. In AQHA classes for Jr. Horses, the rules that state hackamores are allowed refer to this type, not a shanked, curbed hackamore. Reined Cow Horses are also ridden in this type of hackamore when they are young, between their snaffle and two rein stage, eventually going in a full bridle. The old Californio type trainers and hackamore men considered true hackamore riding a high art form. Bosals are often used as starting equipment or in the transition out of a snaffle bit.
There are a variety of bitless bridles on the market. All work on varying principles of noseband or jaw pressure. Generally composed of nylon or leather, they work best for breaking colts or giving a seasoned horse a break from a bit. They do have limited control due to a lack of severity, and finesse and collection may be difficult to achieve.
The Tom Thumb is a bit that gets a bad rap for being very harsh--stories have been passed around of people breaking their horse's jaw with it. Now, that seems a little exaggerated to me (I can't imagine how much pressure they'd have to be exerting on the reins to cause that much damage), and while I don't consider the TT to be particularly cruel, I just plain don't like it for a variety of reasons. Many people do use and love this bit, swearing by it and using it for training colts. To each his own, but my personal opinion is that there are far better bits on the market.
This, right here, is a true Tom Thumb--and the worst one in existence. The straight shanks don't give the horse any warning at all--the second you apply pressure, they pop right around, snatching the curb and activating the nutcracker effect with the mouthpiece. It also makes direct reining difficult--the straight shanks, combined with the way the mouthpiece attaches to the shanks (no freedom whatsoever), mean that when you pull on one side, the entire bit twists rather painfully in the horses mouth. The curved shank versions aren't quite as bad, but it's still quite difficult for the rider to convey the intended cue to the horse, no matter how light or heavy his or her hands are. This bit just doesn't have a whole lot of finesse in the horse's mouth--it's all or nothing. And any efforts at direct reining will likely result in confusion for the horse. While many horses do ride well in a TT, this often has far more to do with the kindness of the horse's temperament than the quality of the bit.
Now compare the above bit to this, your standard Argentine Snaffle.
At first glance, they look very similar. But the Argentine is much better balanced. Look at the curved shanks--these make it less harsh, and a slight touch of the rein will give a horse warning that a cue is coming, giving the horse time to react. Also, the joint between the two parts of the mouthpiece is finished better, so it will be less likely to pinch. Most importantly, the attachment from mouthpiece/shank is not fixed in the vertical direction. This gives both parts some freedom and independent movement. Slight jingles in the reins are often all that is needed to give a cue and thus get the desired response from the horse without the yanking that is often required with a Tom Thumb. Ask any horse--most will respond so much better to bits of this type.
Of course, the "snaffle" mouthpiece in both bits has the potential to "nutcracker" and pinch, so be careful with that. A three-piece mouth is more desireable in most cases. The $5 Grazing Curb
This is the bit that comes free with many cheap bridle sets, or can be purchased on its own for somewhere around $5--which, quite frankly, is about $4 more than it's worth. Sometimes it's made out of stainless steel, but more often it's plated with some strange nickel alloy, which chips and comes off leaving rough edges after everyday use.
This isn't really that harsh of a bit, although you can get quite a bit of leverage between the shanks and curb. The problem is that it's totally unbalanced for a horse's mouth. It just doesn't sit right. Pulling on one rein tilts the bit awkwardly and pulls it through the mouth and into the tongue as well as activating curb pressure. The horse is confused, so he tosses his head and gapes his mouth--at least, this is the typical response. There are absolutely no moving parts on this bit, so direct reining is out of the question. A well-broke horse who knows how to neck-rein will tolerate this type of bit, especially if the rider stays out of his face. Still, nine times out of ten, it's better to just get a different bit. Your horse will be happier, and you'll get a better response. The Junior Cowhorse
The Junior Cowhorse is a moderate gag bit that is popular for the transition between a snaffle and a curb bit in a young horse. The two-piece jointed "snaffle" mouth, three-piece dogbone, and chain are the most common mouthpieces, but there are many other varieties. When used with a leather curb adjusted loosely, it is a very forgiving bit as it gives a signal to the mouth before fully engaging and putting pressure under the chin.
Everything about this bit is in moderation--the shanks are off a medium length, they are slightly curved, and there is only a little curb action. This means that the Junior Cowhorse isn't a particularly harsh bit compared with some others on the market. It also makes it a good transition bit into a gag, draw, shanked, or curb bit.
If you are using this bit as a transition from a snaffle, it is best to start with a leather curb strap and the same mouthpiece your horse is already used to. However, this bit is also used with great success on broke, finished horses as it has a lot of lift and keeps them light. Like many gag bits, it's great for "pick up" and lateral movement, and is popular with trainers, ropers, and other speed event folks.
Sometimes called a "Cut-Tongue Bit" because it works well on horses who have previously injured their tongues and don't respond well to other bits as a result, the Rutledge Roper is a unique take on the shanked bit. It looks more severe than it is, but this is still a relatively heavy bit that should only be used on experienced, broke horses. The shanks move independently, meaning that rein-tightening on one side picks up the shank for that side, enacting the curb more to that side. The broad, flat mouthpiece lies on top of the tongue over a wide area and works off of different pressure points than any other bit. The curb is the first to engage when pressure is applied and the shanks swing back. When it has tightened as far as it can go, the mouthpiece is rolled back onto the tongue. For this reason, the curb should be kept relatively tight to prevent the mouthpiece reaching the vertical and jabbing the thin edge into the lips and tongue.
It serves to put a good rate on a horse. Its design also keeps a horse's head straight and prevents it from over-flexing.
As its name suggests, the Rutledge Roper is used most often by ropers who need a quick, straight stop, or by barrel racers riding extra-bendy horses or those who need help rating. The Josey Combo / "Million Dollar Bit"
This is one of the most commonly used (and mis-used) bits by amateur barrel racers. On the right horse and in the right hands, it can be an effective tool for communicating lift and rate. In the wrong hands, though, it's unnecessarily harsh and confusing.
How does it work? First, there is a considerable amount of gag action, which applies poll pressure, shortening the bridle and bringing the mouthpiece (usually a twisted dogbone or twisted "snaffle") into the bars and tongue. As this engages, however, the curb chain also tightens, and the noseband drops down, putting pressure on the sensitive nasal area. The long shanked version exerts considerable, powerful, painful leverage, but has a slower response time than the short shanked version.
The biggest problems I see with these bits are that, for one, they are confusing, with all of the different actions that can really intimidate a young or green horse. Second, the long shanks can be harsh. Worst of all, any bit or hackamore with a rope (or harsher) noseband can really abrade the horse's face, even with a fairly soft-handed rider. This is particularly true in the sport of barrel racing, where the fast-paced action can lead to inadvertent tugging and pulling, even for a skilled
The main difference between a Boucher and other snaffles lies in its main advantage--stability in the mouth. The smaller rings attach to the bridle, and the reins go on the large rings, like a regular snaffle. Contrary to popular belief, this bit will not apply poll pressure, as there are no shanks and the reins attach at the level of the mouthpiece. The benefit of the Boucher's construction lies in that its attachment prevents the bit from moving about in the mouth and inadvertently annoying the horse.
The Kimberwick is a type of English bit that can be used in two ways. Attaching the reins to the top slot, sans curb chain, turns the bit nearly into a snaffle. Attaching the reins to the bottom ring and using a curb gives you a short-shanked curb bit with mild leverage action.
There seems to be some controversy in the English world as to whether or not Kimberwicks are harsh bits. Yes, they are shanked bits, meaning that a Kimberwick will be stronger than a snaffle with the same mouthpiece. But in the general scheme of things, Kimberwicks are still on the mild side of the bit spectrum, as their shanks are quite short and they don't magnify pressure all that much. Some horses simply cannot tolerate the action of a snaffle, but love a Kimberwick. Also, contrary to wide-held beliefs, Kimberwicks are not intended to be used with two sets of reins. Pelhams
A Pelham is a curb bit with a specific type of shanks, as seen in the pictures above. It is your typical curb, with moderate shanks (and hence moderate leverage action) and would be rather unspectacular--except it can be used in four different ways.
Attaching the reins only to the top ring gives you a snaffle bit, as the shanks are not employed in any way. Attaching the reins only to the bottom rings gives a normal curb bit. Attaching two sets of reins (one to the top ring, and one to the bottom) allows you to adjust how much direct (snaffle) pressure is applied as well as how much collection (curb) pressure is applied. This gives a unique feel and is custom fit to the rider's needs. Attaching Pelham "roundings" to the bit and putting the reins on these splits the bit's action between that of a curb and that of a snaffle.
The tiny center ring on the shanks may be used to tie the sides of the bit together to increase stability and prevent the shanks from flipping up, or it may be ignored.
The lowest curb rein ring is often loose and free-swinging. Though the vibrations produced by this movement may annoy some horses, they also help transmit the feel of even the gentlest lift of the reins--and thus warn of a coming cue. The Weymouth Curb and Bradoon
These bits are meant to be used together and are commonly used in saddleseat disciplines and in the higher levels of dressage, though the double bridle is not restricted to these sports.
The bradoon is like a loose ring snaffle but the cheek pieces are smaller and the mouthpiece is normally finer and narrower. This is the bit that is used for more direct reining and cues along with bending the horse and asking the horse to raise up more in the bridle. This bit is placed into the mouth first and attaches to a second bit hanger.
The Weymouth is a curb bit that is placed lower in the mouth and attaches to the main bit hanger on the bridle. This bit is used for refinement in movement and cues, not direct reining. It is utilized when asking for a higher degree of collection from the horse and also is great to ask the horse to bring their nose down.
If you have never used this set up before and want to, go find a trainer and work from the ground up. When used properly these bits are wonderful, but if not used correctly are easily abused and can damage the horses mouth.