I'm looking for antennas to attach to my CB radio. This one is a "rubber ducky" antenna.
I'm not sure what the connector is, can anyone identify it for me?  Here are some other pictures
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I can't tell for sure without better pictures, but that looks like, not an RF connector per se, but a 3/8"-24 stud. This is very common for CB antennas.
The reason I say it is not an RF connector is because it only makes one electrical contact. This means it can only be used for “monopole” antennas, not for feed lines or other types of antennas.
To confirm, first check that the end of the antenna is solid metal and not anything more complex than that. Then take the antenna down to your local hardware/home improvement store — or your garage, if you're well equipped — and try it against a 3/8"-24 nut.
(3/8" refers to the outside diameter, and 24 refers to the thread pitch in threads per inch. The other common size is 3/8"-16.)
You should not have any trouble finding CB antennas with a 3/8"-24 thread at the base, now that you know what it is called.
It is definitely not a 3/8" connector. 3/8" in in metric units is 9.525 mm. The image at the bottom seems to indicate that is about 6.25 mm which is 1/4". I believe this to be a mobile TV antenna element used by truckers. They usually come in pairs and mounted on the mirrors. The threading is 1/4-20.
A 9.5" in length definitely not CB probably used to receive in the VHF/UHF range.