I am currently reading Archie to SAM - A short operational history of ground-based air defense by Kenneth P Werrell, a former USAF pilot. (The link goes to a download of the book - 5.7 MB)

Werrell relates how the US Navy selected the Swedish 40 mm Bofors anti-aircraft gun and licensed production of it, by Chrysler and another company called York, in the US.

The US government signed a contract in June 1941 and installed the first 40 mm Bofors aboard ship early the next year. But, there were problems in manufacturing the Bofors. First, the original metric drawings had to be converted to English measurements; second, it was found that the two American manufacturers used different systems—York decimals and Chrysler fractions. As a result, parts for the American-made guns were not completely interchangeable. At first 200 parts differed, but this number was eventually reduced to 10.

(Ch 1, p50)

It would be interesting to know if there were other manufacturing problems in WW2 because of difficulties in measurements.

The only similar episode I know of was caused by the Enfield inch, used by the British small-arms manufacturer Enfield for sizes smaller than two Imperial inches. The Enfield inch was 0.0004" smaller than an Imperial inch, and caused a lot of confusion at the Lithgow small-arms factory in Australia when the Australians began making their own Lee-Enfield .303 rifles.

(Originally posted to r/Metric)