Polyamide obtained by the polymerisation of Hexamethylenediamine and Adipic acid. It is one of the oldest engineering plastics, having been created in the USA in 1930. Due to its origin it is widely used in the American and English markets. In comparison to PA6 it is more stiff and tougher but is also more brittle. It is advisable to use PA66 instead of Polyamide 6 when a higher stiffness is required to the detriment of resilience. It can be easily machined on automatic machine tools.