A curb bit is a type of bit, which is part of the bridle that goes in the mouth of the horse, that uses lever action. It includes mouthpiece, curb chain and shank. It has one ring on each side of the purchase arm of the shank and one on the bottom for the lever arm of the shank.

It works on several parts of the horse's head and mouth, which differs it from the snaffle bit. The bit mouthpiece is the part of a curb bit where the curb chain, shanks and straps are attached. It rests on the bars of the mouth of the horse in the delicate interdental space where there are no teeth.

It acts on the bars, tongue and roof of the mouth of the horse. The curb chain, which is the flat linked chain or strap, is attached on either side of the mouthpiece close to the corners of the mouth. This places pressure from the shank to the jaw groove. A curb chain is used to control the lever action of the curb bit.

Also, it helps keep the bit steady and in place within the mouth helping to hold the lip strap in effect. The bit shank refers back to the side piece or cheekpiece of a curb bit. It adds leverage and place stress on the poll through the crownpiece of the bridle. Depending on the length of the curb's bit shank, the curb can amplify rein pressure numerous times over.

Shanks are usually made from metal and are designed either straight or curved. Curb bits come in different styles like Weymouth curb, grazing bit and spade bit, which are the most typical types. A Weymouth curb features a straight shank and a solid mouthpiece with a low port. A grazing bit has shanks that are turned back, generally, almost ninety degrees. A spade bit is a vaquero designed curb bit with straight, highly decorated shanks and a mouthpiece with straight bar, a narrow port with cricket and a spoon.

The severity a curb bit can cause is predicated on several variables,eg the length of the shank. The longer the shank, the more leverage is made and that the more severe the bit can be. Another variable that will add to the severity is the size of the port, which is the area in the middle of the mouthpiece that's often a little raised. The higher the port, the more severe is the bit.

The tightness or looseness of the curb chain also has effects on the scale of the bit. The tighter the curb chain, the more pressure will be felt by the horse when the rider uses the rein. When the chain is tightened, the shank doesn't come back as far and more pressure is felt sooner with this adjustment. However, when the curb chain is loose, the shank comes back further when the rider pulls the rein but the horse doesn't feel the pressure on the jaw area as soon or as much.