Found in a old toolbox with a bunch of Snap on, JH Williams, and various other brands dating between the 40's-60's.
Couldn't figure out what it was till I found it in the 1947 Snap On catalog.
Catalog states it is for use in Black & Decker and Chicago Pneumatic tools to run 1/2" drive sockets.
5/8" hex -> 1/2" drive. 5" long
Pretty obscure, not sure if it much practical use but maybe someone wants to add it to their collection?
No idea what it's worth. Make an offer.