Flipping a two bedroom condo on Cape Cod. I went to install a new ceiling light fixture but could not figure out where on the electrical box to screw in the mounting bracket. I see where it would fit, but there is just a void- nothing for the screw threads to hold onto. What am I missing? Do I have to replace the box or find a longer strip/ mounting bracket and secure that to the ceiling? It’s a very light weight fixture but that’s doesn’t sound like the solution. Is there something like a putty I can fill the voids with then screw into?

@Molly MacGregor YouTube.  Hard to type an explanation, easier to view an explanation.

If you could post a picture it would help.

There are few different sized boxes that are used, but usually a new light will have multiple sets of mounting holes on the bracket to compensate for different lights.

If the tab is broke off the box, you may be able to use something like a toggle fastener to make it work.

Difficult if your existing box is metal, but I would replace with a "old work" ceiling box.
Takes just a couple minutes and is great for a light weight ceiling fixture.

1-Gang 18 cu. in. Round Old Work Ceiling Box

https://homedepot.app.link/uFfMCVvKLJ

Originally posted by @Molly MacGregor :
Flipping a two bedroom condo on Cape Cod. I went to install a new ceiling light fixture but could not figure out where on the electrical box to screw in the mounting bracket. I see where it would fit, but there is just a void- nothing for the screw threads to hold onto. What am I missing? Do I have to replace the box or find a longer strip/ mounting bracket and secure that to the ceiling? It’s a very light weight fixture but that’s doesn’t sound like the solution. Is there something like a putty I can fill the voids with then screw into?

Hi Molly-

Pretty much the same as what has already been posted.  There should be a set of screw holes on the light fixture box in the ceiling that are located on opposite sides of each other.  There are sometimes two holes on each side for different allignment.  Make sure too that the mounting screws you are using are the right size.  If the screws are not wide enough... they will just slide in the slot, and not grab on to the threads.  

Thanks. I will try larger diameter screws to mount the bracket. I’m screwing into plastic. I have a picture but mobile app won’t let me add it.