Apex socket

[wrench136]

Apex Dayton, Ohio. #5518 9/16". Deep reach but not deep well. Well is 3/8" deep. 3 1/4" OAL. Non magnetic.
Is there a special use for this type of socket? Not interested in Apex history. 1/2" drive. 6 point. Thanks.

 

[RTM]

None of the web sites carrying it seem to think it has a special purpose. May not be vintage, maybe ask in general?

apex "5518" socket - Google Search