Respectfully, I don't think it's a CB microphone hook for at least the following reasons:
1) It doesn't have a spring to hold the microphone back clip firmly into contact with the holder.
2) The back button on a typical CB microphone is conductive and connects a circuit that causes the receiver to un-squelch when you remove the microphone from the holder so you can monitor the channel before broadcasting. There is no provision to ground the "mic clip", and the lack of an internal spring would make such a ground connection unreliable (ignoring for the moment there appears to be no such provision to make this connection.)
3) The clip has countersunk holes for its mounting screws. A typical mic clip would use pan head screws or machine screws, neither of which require countersinking.
On the contrary, I can easily picture this as a holder for a door sliding chain-type lock, complete with countersunk screws.
Thanks guys for all replies Red James I'm filing it under door chain hardware, Tommy a hobbit CB, Anduril thanks for the info, old digger that's how I saw it too... Stay warm an Happy Hunting. Snaps