PURCHASE - The part of the bit above the mouthpiece.  With a short purchase, the bit will act quicker in a horse's mouth when the rider pulls on the reins.  With a long purchase, the bit is slower to react. 

SHANK - The part of the bit below the mouthpiece.  Will give you leverage on the mouthpiece.  The shorter the shank, the less control - the longer the shank the more control. 

CHEEKS - The sides of the bit.  Includes both the purchase and shank. 

MOUTHPIECE - The part of the bit that goes in the horse's mouth.
 
DIFFERENT TYPES OF MOUTHPIECES
JOINTED - broken in the middle and one of the most common mouthpieces. 

THREE-PIECE SNAFFLE - broken in two places so as to work on different places on the bars than a regular snaffle. 

DOUBLE TWISTED WIRE SNAFFLE - made up of two small snaffles which are broken off-center from each other. 

CHAIN MOUTHPIECE - does not work on the bars as a snaffle, but on the corners of the mouth. 

SOLID MOUTHPIECE - any mouthpiece that is not broken. 
BARS - Rest on the horse's bars (gums behind the teeth).

PORT - rests on the tongue.  There are high, medium and low port bits.  The closer the bars are together, the more severe, the wider apart, the less severe.

MULLEN RELIEF - a forward curve to the mouthpiece gives even pressure across the mouth.  This causes a smoother reaction from the horse.

SWIVEL MOUTHPIECE - the mouthpiece swivels on the shank.  Allows independent shank action.  Gives the mouthpiece a different action than a solid constructed bit. 

METAL USED IN MOUTHPIECES 

COPPER - Causes a horse's mouth to salivate which allows the mouth to stay soft and usable to the rider. 

SWEET IRON - It is intended to rust.  It actually does have a sweet taste to it as rusting occurs. 

STAINLESS STEEL - Gives a clean, neat look to any mouthpiece. Does not encourage or discourage salivation. 

SNAFFLE VS. CURB BIT
Many riders, tack shops, and even manufacturers confuse bit terms. Snaffle bits are those that do not have shanks like a curb bit, but instead have rings on the side. These rings put pressure on the sides of the horse's mouth while the mouthpiece, which is usually a broken design, puts pressure on the horse's mouth. Because of the lack of shanks, the snaffle bit is a more gentle bit if used properly. Shanks on a bit multiply the pressure that the rider puts on the reins. Without shanks, the snaffle bit delivers the exact amount of pressure the rider uses.


Curb bits, including the pelham and Weymouth, are leverage bits which multiply the pressure put on the reins; the longer the shank, the more severe the pressure. The bit can put pressure on the horse's bars, tongue, and roof of the mouth with the mouthpiece, and also put pressure on the poll and chin groove. The type of pressure each bit produces is dependent on not only the length of the shank, but also what type of mouthpiece is used in the bit, as well as where the bit is fitted into the mouth of the horse.


THE SEVERITY OF A BIT
Exactly how severe a bit feels to a horse is determined by several factors. Though Snaffle bits have been coined the "more gentle" bit, an ill-fitting Snaffle or an inconsiderate rider can still pain a horse. The longer the shanks of a bit, the more potential for pressure. Where the bit is placed in the horse's mouth also affects the feel: the further down in the mouth, the more concentrated the pressure. 

The mouthpiece of the bit is also a major factor in determining how effective (and on the other hand, harmful) a bit can be. Both curb and snaffle bits can be purchased with jointed mouthpieces (the jointed mouthpiece that is often incorrectly labeled as a "snaffle"). Jointed mouthpieces, whether on a bit with or without shanks, can increase the pressure capabilities of a bit. However, with these things in mind, it's important to note that experienced riders can use many types of bits with great success and gentleness with their horses. Inexperienced or heartless riders can do the exact opposite.


OTHER BIT TERMS TO KNOW
THE "FEEL OF THE BIT" - Not only what the horse feels when the rider pulls on the reins; but, also what the rider feels.  For example, suppleness or stiffness. 
TIMING - The amount of time required from the point when the reins are pulled until the bit has done as much as it can do. 

POINTS OF CONTROL
Bridge of Nose        Hackamore 
Chin Area               Curb Chain 
Corners of Lips        Ring Snaffles 
Bars                       Solid Mouthpiece 
Roof of Mouth          Port in a Solid Mouthpiece 
Poll                        Leverage Bits