Is there a word for such thing? Think of a tank or vehicle with a metallic bar projecting to the side and that's used to carry some bag. Is there a name for something like that?
Here's an example:
The ___ embedded into the truck was used to carry John's bag.
In the military, there are many names for things known only to the soldiers familiar with them. I expect, if it exists, there is a specific term for something like this on a tank (although it's not clear why you would put a protruding metal bar on a tank, as it's a potential weak point in the armor), but I have no clue what it might be.
Colloquially you might call such a thing a "strut" or a "spar", depending on its purpose. However, both of these are normally load-bearing, functional items, and not just extraneous pieces sticking out from a vehicle.
So "bar" or "rod" might be better.
I found this, and I think it is similar to (maybe not exactly) what you want:
It was on an online shopping website under the name:
Car Truck Seat Back Bag Hanger Holder
You can ignore the "Seat Back" part as the hanger holder is not normally placed there in vehicles if they happened to have them, but above doors windows. And is popular to exist in public transportations such as buses.
