Do Italian frame sets use different sized components to bikes in the USA?
Some Italian bikes have a metric BB thread but I have a Bianchi that has the standard BSA imperial thread so it's very difficult to tell unless you have thread measuring gauges. There are still a lot of BB assembly manufacturers making Italian threaded versions. As for any other parts they'll have standard European or Japanese (DIN or ISO) metric threads. Steerer tubes are usually imperial and seat posts invariably have a metric equivalent to the imperial parts.