Given the size marks, I'd vote for "inch to metric" adapter shims for sockets and box end wrenches. Dad had a "new old stock" set in unopened blister pack that sold on one of his sales. The theory was cheaper to buy a set of shims than a whole set of metric wrenches. Of course they'd rapidly get lost when you tried to use them.
It's really interesting to me, all the lengths people went to about metric. I grew up in a family that welcomed "foreign" cars when they started to show up in numbers in the U.S., and we always had metric tools. But I do remember, back in the 60s and 70s, that a mechanic who had a full set of both "SAE" - fractions-of-inches - and metric tools was either distrusted as someone who dabbled in those furrin cars or envied as someone who was ready to tackle whatever rolled through the door, depending on the attitude of the observer.
Side note: when Dad sold his car lot in 1965 or so, we wound up with two VW bugs and a Goliath* Sport Coupe, in addition to the trusty Plymouth and, if I recall correctly, something else, because the guy who bought the lot didn't want any of that foreign stuff on his lot. I had my choice of cars from the fleet for the commute to high school.
Seems kind of silly now, in a world in which "foreign" car companies are building their cars in plants located here in the U.S., and "American" cars are built from components assembled all over the world.
Whitworth, now, that's a different matter...
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*The middle line of a German corporation called Hansa, which went out of business about 1963, and thought to be one of the design inspirations for the early versions of the Subaru car: front wheel drive, flat four engine. Spunky little thing, but an unfortunate pink color, which didn't do much for its potential as a date car, in spite of the reclining seats.
