How Horse Bits Work: Snaffle, Curb and Everything in Between

Where a bit puts pressure

A bit sits in a gap in the horse's mouth between the front teeth and the cheek teeth. When you pick up the reins, the bit can press on several places:

• The bars: the bare gums in that gap, over the jawbone. They are sensitive and thinly covered.
• The tongue: a large, fleshy cushion that takes most of the pressure from many bits.
• The corners of the lips.
• The roof of the mouth, if a single-jointed bit folds up into it.
• The chin groove, through a curb chain or strap, on curb bits.
• The poll, behind the ears, through the bridle's crownpiece, on bits with leverage.

A well-chosen bit spreads pressure where the horse can tolerate it and releases it the moment the rider softens. The release teaches the horse; the pressure only gets its attention.

Snaffle bits: direct pressure

A snaffle is any bit where the rein attaches directly to a ring beside the mouthpiece. There is no lever. If you pull with 1 pound of force, the horse feels about 1 pound in its mouth. That direct feel is why snaffles are the standard bit for starting young horses and for most English riding.

A snaffle works mainly on the corners of the lips, the tongue and the bars. Pulling one rein moves the bit sideways and asks the horse to turn its head, which makes snaffles good for steering a horse that's still learning.

Snaffle mouthpieces

Snaffle cheekpieces

The rings on the sides change how the bit sits and moves:

• Loose ring: the ring slides through the mouthpiece, so the bit moves and encourages a horse to mouth it and soften. It can pinch the lips if worn.
• Eggbutt: fixed, barrel-shaped joints that keep the bit stable and won't pinch. A good choice for horses that dislike a busy bit.
• D-ring: a flat side bar presses against the cheek when you turn, helping steering. Common on racehorses and Western snaffles.
• Full cheek: long bars above and below the mouthpiece keep the bit from sliding through the mouth and help with turning. Usually used with small leather keepers.
• Hanging cheek (Baucher): hangs the mouthpiece from a small upper ring, so it sits very still in the mouth.

Curb bits: leverage

A curb bit has shanks, the arms that extend below the mouthpiece. The reins attach at the bottom of the shanks, and a curb chain or strap runs under the chin. When you pull the reins, the shanks rotate. The mouthpiece presses on the tongue and bars, the chain tightens in the chin groove, and the top of the bit pulls down on the poll through the bridle.

Because the shank acts as a lever, a curb multiplies the force from your hands. A bit with a lower shank twice as long as the upper part, called the purchase, roughly doubles the force at the chin and mouth. Longer shanks mean more leverage and slower, stronger signals. Shorter shanks are quicker and milder.

Curbs are meant for horses that already understand the aids. They are used with a light, loose rein and small movements of the hand. In Western riding, a finished horse in a curb is ridden one-handed and neck-reined. In dressage and some English classes, a small curb called a Weymouth is used together with a thin snaffle in a double bridle.

Port and tongue relief

Many curbs have a port, an upward curve in the middle of the mouthpiece. A low port gives the tongue a little room, which moves more pressure onto the bars. Very high ports can press on the roof of the mouth when the shanks rotate, which is why they belong only in experienced hands.

The "jointed curb" trap

Bits with a jointed mouthpiece and shanks, often sold as "cowboy snaffles" or Tom Thumbs, are curbs, not snaffles. The joint folds into a nutcracker while the shanks add leverage, so they can be harsh. They are often marketed as gentle beginner bits. They usually aren't.

Combination bits: Pelhams, Kimberwicks and gags

Some bits mix snaffle and curb action:

• Pelham: one mouthpiece with two rein positions, a snaffle rein at the mouthpiece ring and a curb rein at the bottom of a short shank. Ridden with two reins, or with a converter strap that joins them into one rein, which blurs the two actions.
• Kimberwick (Kimblewick): a D-shaped ring with a curb chain. Lowering your hands adds mild leverage. Popular for strong ponies and horses that get heavy on cross-country.
• Gag bits: the cheekpieces run through holes in the bit, so pulling the rein slides the mouthpiece up in the mouth and adds poll pressure. They are used to lift the head of a horse that leans or pulls downward.
• Three-ring or elevator bits (Dutch gag, Pessoa): a ring snaffle with extra rings below. Attaching the rein lower adds leverage and poll pressure. Common in show jumping.

These bits have real uses with experienced riders. They are also where many horses end up when the actual problem is training, fitness or pain.

Materials

• Stainless steel: durable, easy to clean, neutral taste. The most common material.
• Sweet iron: rusts slightly, which many horses find pleasant; encourages salivation and a soft, wet mouth.
• Copper and copper alloys: warm taste, also encourage mouthing. Pure copper wears quickly, so it's usually inlaid or alloyed.
• Rubber and plastic: soft and light. Good for horses that dislike metal, and for young horses.

How to size and fit a bit

1. Measure the mouth. Use a bit-measuring tool, or put a string or a wooden dowel through the mouth where the bit sits and mark it at each lip.
2. Add room. A jointed snaffle should extend about a quarter inch beyond the lips on each side. Too narrow and it pinches; too wide and it slides around and the joint drops lower than it should.
3. Choose thickness to fit the mouth. Thicker isn't always gentler. Many horses have a thick tongue and a low palate, and a fat mouthpiece fills their mouth uncomfortably.
4. Adjust the height. A snaffle usually sits so it makes one or two soft wrinkles at the corners of the mouth. A curb usually sits a little lower, with no wrinkles. Adjust the curb chain so two fingers slide under it and the shank rotates about 45 degrees before the chain engages.

Most adult horses wear a 5-inch bit. Arabians and small horses often take 4.5 or 4.75 inches, and big warmbloods and drafts 5.5 inches or more.

Choosing the right bit

Work through these questions with your trainer:

• What is the horse's training level? A young or retrained horse belongs in a plain snaffle.
• What are your hands like? A rider who still balances on the reins should ride in the mildest bit possible.
• What does your discipline allow? Dressage, hunter and Western show rules restrict which bits you can use, and some divisions require a snaffle or hackamore for young horses.
• Is the problem really the bit? Head tossing, gaping, getting the tongue over the bit and pulling can come from sharp teeth, wolf teeth, back pain or a poorly fitting saddle. Have the teeth checked before you change bits.

If you want to try riding without a bit, read our guide to hackamores and bitless bridles. And when you're shopping, our snaffle bit picks are a good place to start.

Sources

• Oklahoma State University Extension: Bit Selection for Riding and Training Horses
• Utah State University Extension: Bitting the Horse: Snaffles
• University of Georgia Extension: Bits 101
• Michigan State University Extension: Understanding Bits and Bridles