Wrought Iron is the purest form of iron; although it may contain traces of carbon. It is usually made by ‘‘puddling process’’. It is very costly and its use has been almost totally replaced by cheaper steel. However, for some components like chain-links and Crane-hooks wrought iron is still the preferred raw material.

Poise is the unit of dynamic viscosity. It is named after the French physicist Jean Louis Marie Poiseuille, who made important contributions to the study of fluid mechanics. The dynamic viscosity is a measure of a fluid's resistance to flow when a force is applied to it. It is defined as the ratio of the shear stress to the shear rate of the fluid. The poise is a CGS (centimeter-gram-second) unit of dynamic viscosity, and it is equal to one dyne-second per square centimeter. Another commonly used unit of dynamic viscosity is the Pascal-second (Pa·s) in the SI (International System of Units) system. One poise is equal to 0.1 Pa·s.