Horse's bits can be made out of different materials, New bits are usually made out of Stainless Steel. Old bits used to be made out of Nickel. These bit are regularly sold second hand. They can go brittle over time, but some horses prefer the taste of nickel.
Brass Alloy - These are a light brass colour and have a taste which can encourage horses to soften.
Copper - These are usually coated in copper and again the taste encourages salivation.
Sweet Iron - This is another material to encourage salivation, as this causes the bit to rust producing a nice taste.
Synthetic - These are soft on the horses mouth and very light, they can come with apple flavour.
Rubber - Rubber covered mouthpieces are generally very thick soft bits.
Hard Rubber - This is hardened by heat and are more hard wearing than normally rubber but are still very thick soft bits.
Vulcanite - This is a hard plastic which is tough and give the bit a thick soft action.