[Boatanchors] unknown connector

[Dick KF4NS]

Maybe someone here has seen one of these but it is new to me. I have a 
BNC male thingy with a 3/8 inch threaded metal hexagon stub 3/4 inches 
long as part of the connector. It does not have DC continuity so I 
tested it with my LCR meter and it reads about 15pf.

What would this be used for and does it have a name. (other than 
thingy?)

Thanks and 73, Dick KF4NS
St Petersburg, FL 33714 USA
Keep The Glow!