Can anyone tell what these screws in my upstairs ceiling are for? There are three drilled into a joist, about 1.5 ft from a window.
I would guess they are for some style of curtain rod. But I don't understand why it'd be so far from the window. I've also never seen a curtain rod that mounts to the ceiling...
In case I can't figure a use for these, any recommendations on removing? There is no head to turn with a screwdriver.
Terminology-wise those look like bolts. Removing-wise, look in the attic above the room for bolt-heads, first. If they are not though the joist, they are probably a "lag/machine combination", and you put two nuts on, tightened against each other, then use a wrench on the upper one to back them out. Putting them in is the same, but you put the wrench on the bottom one.
Use-wise, something hung from the ceiling, probably somewhat heavy - punching bags, for one example. Hanging/hammock chairs for another. Majorly overdone chandeliers...
The type of bolt that you show and the size comparison that you demonstrate in the second photo would indicate that these were installed for ceiling hooks of the type pictured below:
Indeed if the ones in your ceiling seem solidly placed then the hook was installed using the ceiling joist type of bolt/screw as shown in the right part of the picture. The other toggle bolt type is used when mounting the ceiling hook when there is and open space above and depends just on the drywall for support.
It would seem that a previous occupant simply unscrewed the hooks and left the bolt/screw part in place.
This type of hook is most often used for hanging lamps of the type with a swag chain (type of lamp hung from a chain with the lamp cord threaded through the chain).
The hooks are also used for hanging plant pots. It is possible that this may have been the case in your place since they were installed near the window. Although there is nothing to keep people from hanging lamps near a window as well.
If you do not care about the bolts and wish to remove them by the simplest method you can clamp on to them with a tool similar to the type shown below and just turn it out. Note that this type of removal will crush the threads rendering the bolt/screw part not suitable for re-use.
To remove the header bolts without locking pliers, one can attach two nuts of proper size, tighten them against each other. Apply a wrench to the top most nut and back the header bolt out of the ceiling.
To recap what others have suggested, the easiest thing would be to grab with locking pliers (“vise grips”), especially since you don’t mind smashing the threads. You can supplement that by running a file on one side to flatten it—just a tiny bit (a few draws from a metal file or some buffing with a fingernail stick) can make enough difference that you can grab it.
If there’s enough screw showing, the two nuts locked together is a good approach, assuming you have nuts that fit and a box wrench that’s thin enough to hold the inner nut (and/or enough room to work).
Another way that’s quite robust would be to cut a slot on the end, turning the stub end into something that can take a flat-blade screwdriver. This is easily done with a dremel tool.
Not sure what they were for other than mounting something to the ceiling.
As for removing them, I'd first try clamping a locking pliar on to it and seeing if you can turn it and remove it.
If that fails you might need to cut it flush with a grinder or hack saw. Either way you will need to do some patching and painting.
