Bit Terms
Purchase: the part of the bit above the mouthpiece. This affects both the timing and the leverage of the bit.
Cheeks: sides of the bit. Includes both purchase and shank.
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.
Port: describes the amount of curve in a mouthpiece of a curb bit. (i.e. high, low, medium)
Bar: is the straight portion of the mouthpiece, between the purchase and shank.

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: intended to rust. It has a sweet taste to enhance salivation.
Stainless Steel: has very little taste and creates the least salivation. Has a clean, neat look.