Eli Whitney
As early as 1798, Eli Whitney had turned his talents to the manufacture of firearms. He had established his machine shops at Whitneyville, near New Haven; and it was there that he worked out another achievement quite as [important] as the cotton gin: namely, the principle of standardization or interchangeable parts.
American manufacturers quickly embraced interchangeable parts. Henry Ford was proud to proclaim that no files were used on his production line, all the parts fitted perfectly, and were interchangeable. This had the further advantage that spare parts could just bolt in, again without rework.
There are significant intial costs in mass production, drawings have to be very carefully prepared with all dimensions and tolernaces specified in great detail, and components made to higher tolerances if they are to be assembled without rework. Often tooling, parts which must be manufactured in order to manufacture and form other parts, must be made. Consequently the start up costs are much higher.
In 1930s while Germany was stamping out the first Beetles priced so that workers could drive them on the new autobahns, the British car manufacturers were still proudly elitist and held on to methods which called for a level of ‘fitting’ during assembly. This approach was presented as a virtue, the low volume luxury car makers held that their cars were built by craftsmen and this was promoted as exclusivity.
The British aircraft industry of the 1930s worked in a very similar way to its car manufacturers. And, borrowing the rational, they held that skilled fitters were essential whenever airframes and aero engines had to be manufactured. When the war was imminent and the British government wanted to increase aircraft production big problems were encountered when experienced mass producers attempted to adopt the aircraft industries' drawings and processes. Even relatively straight forward sub-assemblies such as bomb racks, when sent out to be manufactured by manufacturers such as Hoover and Electrolux, created problems. The supplied drawings were not always complete and tolerances were insufficient to define parts that could be assembled without extensive hand rework.
The subcontractors ended up redrawing the original blueprints produced by the aviation big boys such as Avro and Handley Page to the standards that were customary in vacuum cleaner manufacture!