Although materials based on carbon steels are used for molds, some times non-ferrous metals of non-metallic materials are used for molds for the purpose of thermal insulation. At the time of assembling molds, although it is possible to adjust the dimensions at room temperature, since the temperature is increased and decreased during injection molding, the parts tend to undergo thermal expansion (either linear expansion or volume expansion). If the margin for expansion is not considered, the operation of the mold can become bad or the parts can break. The following data is available for the linear thermal expansion coefficients of materials.