Threads used on Early German/Austrian lens flanges?

When did metric threads become the Universal European standard. I ask because all the early (1850's and 60's) catalogues from Voigtlander and others still use the Continental version of the "inch".

I raise this because I am trying to get hold of a missing flange for a 1858 Voigtlander - which really looks like a 4" thread, rather than a metric size. The metric size was Napoleon's creature, so perhaps there was some delay in it becoming a European standard due to long memories of the wars at the start of the century!

I note that Grimes writes (website) that some European lenses have Imperial thread flanges "Due to export concerns". Perhaps they were just standard lenses?

I have done a quick check on a Waibl (Vienna) lens from the same period - this appears to have a 4" flange too.