Cast iron is used, as the name implies, in ‘castings’, for which the molten metal is poured into suitable moulds and allowed to solidity. This method makes it possible for intricate shapes to be formed with-out the expense and waste of material that would be involved in machining them from a solid block of material. Limitations in the shape and use of such castings are imposed by the relatively low tensile and shear strength of the material. These could lead to cracks in the cast iron as it cools down in the mould, or to the breaking-off of thin projections when it is in use.