Same here Don.I have quite a few plugs but don’t recall any with that odd configuration. All of the retaining balls on mine are inline.
-Don
It's don't think it's big enough for 7/16, but, I tried it in several modern 3/8 sockets, and one side fits perfect while the other side is too big.Is this one stepped and not 3/8” at each end?
Might be Blackhawk if 7/16” ?