What Britishisms most baffle Americans? What Americanisms most baffle Brits?

I’m currently reading Israel Rank – the book Kind Hearts and Coronets was based on. Since it was published in 1907, there are a lot of words and phrases I’m unfamiliar with. I’m reading an annotated edition which has footnoted a lot of things the editors thought needed explanation. Most are helpful, but does Scotland Yard really need to be footnoted?

But one word – not footnoted was pinchbeck, and it was used more than once. I had to google. Turns out it was the name of a particular gold blend used for jewelry and invented by a jeweler named Pinchbeck. Anyone ever heard this word? My edition was published in the 80s, so was that recent enough that the average reader would know what pinchbeck was?