In casting, a pattern making is a replica of the object to be cast, used to prepare the cavity into which molten material will be poured during the casting process.
Pattern making are able to produce suitable patterns using "Contraction rules" (these are sometimes called "shrink allowance rulers" where the ruled markings are deliberately made to a larger spacing according to the percentage of extra length needed). Different scaled rules are used for different metals, because each metal and alloy contracts by an amount distinct from all others. Patterns also have core prints that create registers within the molds into which are placed sand cores. Such cores, sometimes reinforced by wires, are used to create under-cut profiles and cavities which cannot be moulded with the cope and drag, such as the interior passages of valves or cooling passages in engine blocks