snap-on 5/8 drive socket - WTH?

[hedjhawg]

So I picked up a few old Snap-On impact sockets yesterday. I brought them home, cleaned them up, and notice that this one is odd...

It has a knurled ring around the outside, and the drive hole is bigger than 1/2, but smaller than 3/4... 5/8 ?

There is another thread right now about a Blackhawk 7/16 drive. Did Snap-On make a 5/8 drive? The number on the side is impossible to read. it looks like "30C"

Any guesses what this is?

 

[FoMoCoPower]

Yup,it`s OLD,and 5/8" drive.

 

[snapmom]

Its a socket from the late 20s. not a impact.