The pin is recessed and about 1mm in diameter - which seems impossibly small for 6.67A.
Because it doesn't carry 6.67A. What you have there is a laptop power supply, probably an HP or Dell one. The current is carried on the inner and outer sleeve of the barrel. The centre pin only carries communication signals.
But you are correct - there does seem to be a recessed metal inner sleeve. I had looked for one, but couldn't see one - tried again after your post (with a brighter light!)
I still need a chassis mount socket for it, though....
There is a 12v car lead - which makes me wonder if that centre pin is actually used at all...
I guess you could check if it's a physical fit for an HP (or Dell or Samsung) one and then go to ebay or aliexpress and buy a corresponding "laptop charger socket". Though they're all board mount. I don't know if any panel mount ones even exist.
Brilliant! Thanks you so much for taking the time and effort to help me with this - and for mentioning "CONNECTORBOOK.COM" so I can add that as a useful reference. Not a chassis mount but that always was a mission impossible to find, I suspect.