Jonzjob, yes, the pipes are even numbers, but do the french actually say 16 mm, or do they say 1.6 cm?
The plumbing question is easy to answer. between america and the UK, we invented modern plumbing. All pipe and thread sizes were in imperial.
after almost 200 years, just try to imagine the number of old taps with imperial thread. It would cost the GDP of a medium sized country to throw all those old taps away.
I was fitting copper piping when mr smith screwed the world and we had to go to metric thin wall rather than english thick wall. THAT was fun, having to match different pipes all over the house with adaptors.
For one of the ultimate stupidities of mixed measurements, heres a goodun.
kawasaki motorcycles are metric thread. Obvious, the parent company is japanese. But they use two different metric threads, Fine, and Coarse. Both metric, both with the same measurement, but you just try to put an 8 mm fine nut on an 8 mm coarse thread.
It gets better.
That same motorcycle company makes liquid cooled engines. The temperature sensor and oil pressure sensors are not metric thread. The sensors are not made by kawasaki, they are bought in from a USA company. That thread is US 3/8"NPT.
Funny old world, innit?
