Many different materials can be used to make key stock (including machine keys). Key stock is often constructed of carbon steel or stainless steel, although it may also be made of aluminum, brass, copper, monel, and even nylon, all of which have varied material grades. Some manufacturers sell separate key blanks for each type of stock they offer. Carbon steel is by far the most common material used for making key stock. Because this material is relatively easy to work with, it is generally preferred over other materials for this application. Stainless steel is a second-most common option; although it is harder to cut than carbon steel, it is more resistant to corrosion and wear-and-tear. Aluminum, brass, copper, monel, and nylon are less commonly used options. The exact composition of key stock varies depending on what quality it is intended to produce. Generally, lower-quality key stock is not as hard and wears out faster. However, it can still be used in low-security applications where durability is not critical. Higher-quality key stock is usually harder and has greater resistance to wear-and-tear. It is also usually more expensive because better quality stock needs to be thicker and take longer to cut. There are two main types of carbon steel key stock: plain carbon steel and hollow-ground carbon steel.