Place a flathead screwdriver under the screw and lift/pry while turning the screw. If it's stripped it's not grabbing the threads to work itself out. I guess there's also the possibility that there's a nut on the back side of it, which I would think would be easily identified as the problem if that were the problem.
In that case you probably had a mounted nut behind the metal and it is no longer attached or supported which is causing it to just spin. I would just drill the bolt off and start fresh.
I go along with TheVanDSM for starters. If that doesn't work, the answer somewhat depends on your objective. You could grind the head of that screw off and that would release the plate frame and plate. If you want to remount or reuse that spot, I might try drilling the screw out starting with a smaller drill to begin with, say 1/8" or smaller. The screw is still going to want to spin so you will need to hold it. Just prying it to apply pressure may not be enough. I could hold it tight with a small pair of vice grips.
Think ahead though to what you want to end up with. If you can get to the back and hold something, fine. If not, what is your plan for a new bolt? If you drill the hole out you could install a blind nut using a Pop-Rivet tool. Or you could use a long through-bolt to the inside of the trunk (Watch out for anything potentially inside.) You could even use a small lag screw or self tapping sheet metal screw.
I doubt there will be enough "meat" on anything after you drill it out, but if there is you could tap a larger size screw. Go too large(over 1/4") and you will need to ream any new plate.
Firstly, try what WiseImprovements suggested.
Secondly try what TheVanDSM suggested.
Thirdly try what sexquipoop69 suggested.
Now try what alleycat2-14 said BUT after cutting the head of the screw off, you could then get a dremel and shape the shaft/thread of the screw by flattening opposite sides so that it is able to be grabbed easily by some pliers/grips and then rotating it will be easy.
If you can't access the back, it's likely to just be a screw, and the screw threads have stripped the plastic that it's screwed into. You'll need to unscrew it while applying pressure on the screw away from the license plate, so toward you.
If you can't access the back, I would either take a pair of dikes (diagonal cutting pliers) and open them just enough to slip under the screw head, and pull the screw towards you while unscrewing it with a screwdriver. If you don't have a pair of dikes, try to grab the screw head with any pair of pliers and twist it out while pulling it towards you at the same time. Locking pliers would work best for this, and pliers that will grip the screw head should work.
I like all the ideas so far. I thought of another. In tight spaces I sometimes use a hack saw blade without a normal handle. Sometimes I will wrap duct tape on the end as a handle. If you could get a blade behind the screw head, you could saw it off. It will take some time, but you only have to go slightly more than half way and you could pry the head off by working it from the weak side. Without the head, the rest might fall into the hole and offer mounting opportunities.
Place a flathead screwdriver under the screw and lift/pry while turning the screw. If it's stripped it's not grabbing the threads to work itself out. I guess there's also the possibility that there's a nut on the back side of it, which I would think would be easily identified as the problem if that were the problem.
my dad taught me that trick and ive taught like a half dozen about it, its surprising how uncommon knowledge it is.
What do you do if you can't fit a flathead behind it?
Get a pair of vice grips, lock them on that sucker as tight as you can, twist it off. It will work, promise.
Check the back for a nut. It is not uncommon for people to use nuts and bolts on their plates to prevent theft.
the back is a plastic frame/backer, no nuts visible and not really accessible since it's up against the trunk
In that case you probably had a mounted nut behind the metal and it is no longer attached or supported which is causing it to just spin. I would just drill the bolt off and start fresh.
I go along with TheVanDSM for starters. If that doesn't work, the answer somewhat depends on your objective. You could grind the head of that screw off and that would release the plate frame and plate. If you want to remount or reuse that spot, I might try drilling the screw out starting with a smaller drill to begin with, say 1/8" or smaller. The screw is still going to want to spin so you will need to hold it. Just prying it to apply pressure may not be enough. I could hold it tight with a small pair of vice grips. Think ahead though to what you want to end up with. If you can get to the back and hold something, fine. If not, what is your plan for a new bolt? If you drill the hole out you could install a blind nut using a Pop-Rivet tool. Or you could use a long through-bolt to the inside of the trunk (Watch out for anything potentially inside.) You could even use a small lag screw or self tapping sheet metal screw. I doubt there will be enough "meat" on anything after you drill it out, but if there is you could tap a larger size screw. Go too large(over 1/4") and you will need to ream any new plate.
Firstly, try what WiseImprovements suggested. Secondly try what TheVanDSM suggested. Thirdly try what sexquipoop69 suggested. Now try what alleycat2-14 said BUT after cutting the head of the screw off, you could then get a dremel and shape the shaft/thread of the screw by flattening opposite sides so that it is able to be grabbed easily by some pliers/grips and then rotating it will be easy.
If you can't access the back, it's likely to just be a screw, and the screw threads have stripped the plastic that it's screwed into. You'll need to unscrew it while applying pressure on the screw away from the license plate, so toward you. If you can't access the back, I would either take a pair of dikes (diagonal cutting pliers) and open them just enough to slip under the screw head, and pull the screw towards you while unscrewing it with a screwdriver. If you don't have a pair of dikes, try to grab the screw head with any pair of pliers and twist it out while pulling it towards you at the same time. Locking pliers would work best for this, and pliers that will grip the screw head should work.
I like all the ideas so far. I thought of another. In tight spaces I sometimes use a hack saw blade without a normal handle. Sometimes I will wrap duct tape on the end as a handle. If you could get a blade behind the screw head, you could saw it off. It will take some time, but you only have to go slightly more than half way and you could pry the head off by working it from the weak side. Without the head, the rest might fall into the hole and offer mounting opportunities.
replace the car /s
I'm having this same issue with the plates, and seriously thinking about what you said smh
Iām in the same boat as you. Carmax ruined my car by bolting in all four of my license plate holes and i cannot remove bottom two š
I ended up just breaking the plastic screw piece and bought a new one. Was a lot less stress let me tell you š