The double bridle is known for using two bits, the bridoon and curb, in the horse's mouth at one time. They are designed to work together in symmetry to create a desired head and neck position. When used correctly these bits will refine and finesse the communication between the rider and horse.

Riding in double bits should only be introduced once the horse is working forwards into the correct outline, and engaging their hindquarters in the snaffle bridle. It must never be used by novice riders, or to create a false head carriage on the untrained or young horse. This bridle must only be worn with a cavesson type noseband, and if fitting a running martingale it should be attached onto the bridoon reins.

Today the use of double bits is more commonly seen in the higher levels of dressage and eventing, plus in specific show classes. In British Dressage this bridle is permitted to be used from elementary level upwards, but is compulsory in the higher level tests. For British Eventing a double bridle is only authorised at Intermediate Novice and above, however it is not compulsory to be used at any level.

Each one of the two bits fulfils a different role and should be used independently of each other to maintain flexion of the equine's head and neck, whilst encouraging self carriage. The horse requires comprehensive training to enable them to fully understand the variety of actions and signals these bit provide. When riding, the contact should always be maintained on the bridoon reins and pressure applied on the curb only when necessary.

Typically the bridoon and curb bits are purchased together as a pair, as the length of the two bits are directly related with each other. This ensures they fit correctly in the equine's mouth. Depending on the horse's needs and mouth conformation they are available in a variety of styles.

The Bridoon Bit:

To ensure both bits fit in the horse's mouth, the bridoon bit has smaller cheek-rings and is a thinner version of an ordinary snaffle. Due to its thin structure, it is not designed to be used alone. It is available in a variety of metal mouthpieces, which can either be single or double jointed, plus have loose or eggbutt cheek-rings depending on the equine's requirements.

In order for it to sit comfortably in the mouth it should be ¼ of an inch longer than the curb bit, and be fitted slightly higher than an ordinary snaffle.

The bridoon acts to raise and flex the horse's head, and should always be the predominant bit in use during ridden sessions. This bit works on the same areas, and in the same way, as a normal snaffle therefore choosing the appropriate style for each horse is the same as for the snaffle.

The Curb Bit:

Otherwise known as the weymouth, this bits works on the horse's tongue, bars, poll and chin groove. Its main purposes are to lower and encourage the head towards the vertical, plus help relax the lower jaw when the curb chain is activated.  

This bit should be fitted at the corners of the mouth, below the bridoon. The curb chain should sit flat onto the chin groove and be secured at the correct tension.

Consisting of a mouthpiece, upper cheeks, shanks, a curb chain and lip-strap, each of these key features have an overall effect on the action of this bit. As it is  available in multiple variations, conformation of the horse's mouth and way of going will influence which style is chosen.

The mouthpiece can be straight, applying more tension onto the tongue and bars, or mullen-mouthed to offer more tongue room and release the pressure off the bars. A central port or tongue groove also provides extra room for the tongue, therefore are good for equines with larger tongues or prefer more room in their mouth. In general thicker mouthpieces are deemed the mildest, however those with a large tongue or low palate may find it uncomfortable to wear. Fixed mouthpieces encourage a still mouth, whereas ones which have a sliding moveable effect will increase the activity in the mouth. It is also available in a variety of metals which can increase or decrease mouthing.

Upper cheeks and shanks are fitted on either side of the mouthpiece. When contact is applied on the bottom rein the shanks tilt backwards which activates the curb chain to relax the lower jaw. It also tips the cheeks which pulls on the cheekpieces and headpiece to initiate pressure on the poll. Both the cheeks and shanks can be of varying lengths and it is this which determine the amount of leverage this bit offers; the longer the shanks the more leverage it gives and the stronger the action.

A curb chain is attached to either side of the back of the bit, via links. It should lie flat against the chin groove, free from twists, and secured at the correct tension as it is this which controls the strength of the bit. When a contact is placed on the bottom reins, the curb should act against the chin groove when the shanks are rotated at an angle of 45°. If the curb chain is fitted too loosely the bit will be allowed to rotate too far in the horse's mouth, thus creating large amounts of pressure on the tongue and bars. This will be seen by the shanks rotating more than 45°. When fitted too tightly the action will be very severe, putting vast amounts of pressure on the poll and lower jaw.

Furthermore, the design of the curb chain can also affect its strength. The two metal curb chains are the single link, which is the most severe and rarely used today, and the double link which is a popular choice and commonly used. If the equine is too sensitive for a metal chain leather, elastic, or gel curb chains are also available offering a milder effect against the horse's jaw. For short term use, a rubber guard can be fitted over a metal curb chain.

In conjunction with a curb chain a lip-strap should be fitted, attached to either side of the shanks, and is threaded through the fly-link on the curb chain. It serves several purposes: it helps keep the curb chain in place preventing it from rising, it stabilises the shanks to keep them in alignment and also prevents the horse from getting hold of the shanks with their teeth. When the bridle is removed it stops the curb chain falling off the bridle and getting lost.