Cast iron is iron mixed with much larger amounts of carbon than plain carbon steels. Grey cast iron is the most common type of cast iron, and has a carbon content of 3.5% together with other elements in small proportions. Cast iron is used because it is very fluid when molten, which enables both large and intricate castings to be produced. Cast iron is quite brittle and has the quality of self lubrication. This is due to the excess carbon within its structure allowing both the above to take place. Grey cast iron is used extensively for the production of pre-machined parts. For example motor car engine blocks, crank shafts, gear wheels, pulleys, machine tool bed / frames, etc. Grey cast iron can also be used for marking out equipment such as angle plates, vee block and surface tables. BS1452 specifies seven grades of cast iron numbered 10, 12, 14, 17, 20, 23, and 24, grade 10 being the weakest and grade 24 being the strongest. Some idea of the properties of grey cast iron can be obtained from the table below.