Odd adaptor. What is it?

[ppppenguin]

The PL259 plug isn't too bad if you can get a decent crimp version. The BBC used a crimp adaptor for the braid that screwed into the back of the standard plug. They were rugged and well regarded in TV broadcasting, especially for OBs. The BNC was a bit vulnerable by comparison. The common variety with reducers were truly evil. Impossible to wire them well.