Mystery socket sizes?

[Richard Farrant]

Originally Posted by Harry Moon

I picked up a set of 1/2 drive sockets yesterday, vintage and i cleaned them up and sorted them for my mechanic displays.
So I'm sorting these and can't understand the sizes. Made in USA so I didn't write them off as some eccentric (but perfectly logical, no offence) British thing
As marked and then measured and tried on various nuts and bolts.
marked 1 1/16 = 1 5/16
1 5/8 = 1 1/4
9/16 = 1"
1/2 = 15/16
5/16 = 5/8
3/16 = 15/32
1/4 = 17/32

Any explanation?

British Standard Whitworth ! I have some large 3/4" drive sockets from wartime period, made in USA, think they are Snap-on