Odd shaped 3/8 in. socket

[19Fordy]

I found this 3/8 in. drive socket with both flats and hex. I never saw one before. It appears that it was originally made as a hex socket but, then went through one more manufacturing step whereby every other raised hex was pressed down and removed. The only marking is USA. No size is specified but, it measures 1 in. across the inside flats. Any ideas as to its maker or origin? Thanks.