Actually it's very easy to say that the Metrics are sloppy because then are when compared to the fit of Imperial threads. A company I used to work for had the contract to make and supply all the special bolts for the Bugatti owners club. They have all sorts of weird sizes. One could make the bolt to the ring and gap gauge as well as checking with O-Vee wires and then make the nut so suit using the gauge and when you put the nut on the bolt it wobbled about. Very sloppy. Compared that to say a 5/16 UNF or 4 BA thread and they fit together, that is nut and bolt of the same size, very nicely.
Like most things that the EU has to do with it's a con. We were told that the Metric system was easier and better. One didn't need all these special threads .......... that the Imperial systems had......................... Bull hicky. That's why we have all these speacial Non Standard threads for cars etc because the std ones are no damned good.
They have been forcing it upon us by any under hand means they can because lots of people were not interested in changing. One thing they are doing is making it more difficult for ordinary people to get imperial fastenings. However that's another tale.
Me i'll stick with Imperial threads and if I make something it will have imperial threads the SI lot can go take a very long walk off a short pier.
Brithunter, the standard "M" series metric thread does have a more generous tolerence then the equivalent imperial or unified thread but you cannot group all metric threads under the same "sloppy fit" banner.
There are also fine, extra fine and super fine series of metric threads which are governed by 5 ISO fit standards and just like any imperial or unified thread, they can be cut to very fine tolereneces.
I am not surprised that you had all sorts of sizes of threads for the bugatti owners as the french had there own fit standards, ISO standardization of metric threads happened some years after bugatti ceased production.
As for the modern motor industry out side of the USA it exclusively metric now my friend, the only reason why unified is hanging on in the states is because of the massive domestic market,, if more US made cars were exportd world wide they would all have changed to metric threads years ago.
You cant possibly say that the metric system has been forced upon us it was already the excepted standard in general engineering when i did my apprenticeship back in the late 1970s, also, remember decimalisation of our currency? long time before the formation of the EU or are you hankering for the old pounds shillings and pence?
Ian.

