What size is this wire?

I tore my truck apart today and didn't find anything that looked like coax under the driver's side liner. I did, however, come across a wire that looks like coax, but smaller, that connects between the amp and the antenna for the old car phone setup that's installed in my car (and which I'm currently removing; maybe I can sell it on eBay or somethin'). The ends are too small to screw onto a CB radio, but they look a lot like coax connectors.

I'm wondering if this is maybe the wire that you're referring to, and it was just removed from where it's supposed to be and re-used as this in my car.

Thanks in advance! I like where you put your radio...is the bracket that came with the radio screwed directly into the carpet, or is there some sort of mount like what Richard linked to?