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The introduction to RSAF, in 1856, of the new machines from America and the system of producing interchangeable components that were all identical was a step change in the concept of engineering manufacture in the UK. Since then components have been made by precision machines to very closely controlled dimensions specified on a drawing.

One effect of that change was the need for a precise reference standard of length. When components were being made to match physical patterns, there was no need for precision measurement against a defined standard. However, when all components had to be machined to precise dimensions and gauges had to be made to even higher standards of precision, availability of a high precision reference standard of length became absolutely indispensable, but no such standard existed to the necessary degree of accuracy. RSAF had therefore to acquire a suitable standard to support the new method of manufacturing and thus was born the Enfield Inch.

In America the same considerations forced the same solution, but unfortunately the standards adopted were not all precisely the same and this was to lead to some international friction, involving RSAF, between armaments factories and machinery manufacturers in various countries in later years, notably England, America, Australia and India. In Britain, the Enfield Inch became a de-facto national standard until it was superseded by the Imperial Standard Inch and later the British Standard inch, which is very slightly larger by about 0.0003. Several of the standard Enfield Inches were produced for manufacturing, inspection and reference purposes and one of these is now held by the Pattern Room as part of its collection.

The saga of the Enfield inch in relation to Australian rifle production involving American machines and gauges made to their, slightly different, standard inch has been researched and written up by Tony Griffiths in Australia in his small book The Enfield Inch & The Lithgow .303.

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