Wouldn't think it would be in 1/2" drive but aren't there extra strong sockets for working on dozer/tank treads?
It looks pretty old. Some old sockets are different designs than modern sockets.
I also think it has to do with strength because if I'm going up to 1/2 drive clearance is not usually the issue especially when I'm dealing with a 9/16 or smaller bolt.
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The plating sort of looks like it could be cadmium. Cadmium plating tends to be a dull grey. Be careful if cleaning it because cadmium is toxic. It was used on some older tools in the 30s and 40s as well as for military use do to the dull non reflective surface. It beuing an older socket might also explain the thickness.

None of the numbers you listed are active part numbers. Current 1/2 is P3216, 15/16 OD on drive end and 13/16 on working end. That's an old socket.
Maybe someone too all the black coating off??
Yup,Cornwell could probably help, seeing as they're are private family owned company. Their records should be pretty good I would think.
It is an older socket, considering it is USA made Cornwell. It is also most likely an impact, because it is thicker. They put the taper on the end to help get in to slightly cramped spots. A lot of modern sockets have a similar taper, but with advancements in manufacturing processes, they can be thinner.