The method of manufacturing introduced in the early 1800s that made mass production possible was the use of interchangeable parts. This innovation allowed parts to be made to precise, uniform standards so they could be easily replaced or assembled without custom fitting. Prior to this, products were hand-crafted with unique parts requiring skilled artisans. Interchangeable parts enabled the use of less skilled labor and mechanized production, drastically increasing efficiency and consistency in manufacturing

. Eli Whitney is often credited with popularizing this concept in America around 1803, initially for muskets, although the idea had European precedents such as Honoré Blanc in France. The system was first applied on a large scale at the Portsmouth Block Mills in England for ship rigging components. This method laid the foundation for modern mass production and assembly line manufacturing, as later exemplified by Henry Ford’s automobile production

. Thus, the correct answer is:

• The use of interchangeable parts