"Robin" wrote in message
...
I'm surprised he didn't wonder why there were two sets of apparently
identical allen keys to choose from in the shop.

There were not identical. He "paid for the most expensive of the two".

And they were the more expensive because they probably sold in smaller
volumes and came from a more specialised supplier.

If they aren't clearly labelled and if you have never learned that imperial
sizes are still sold, you would tend to think they were identical apart from
one being "better quality" than the other.