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I purchased some flush mount light fixtures to install in each of the bedrooms in my house. Originally I picked up some circular 4" old work electrical boxes (the ones with the "flags") but discovered that those are not mean to bear weight (the weight of each fixture is about 5lbs). I found the "right" circular old work electrical box which had a metal support and said it supported up to 10lbs, so I bought them and installed them. I did notice that they were 3 1/2" but I didn't think anything of it.

Now I'm trying to install the mounting bracket for the light fixture and it is too wide for these boxes... The outer screws which must go in the outer holes are touching the plastic of the box itself. I feel like I'm screwed now. If they make bigger electrical boxes, I could buy them, but I already have three 3 1/2" holes in my ceiling so removing them and expanding the holes will be a nightmare. These fixtures are meant to match others that I was able to install in original electrical boxes without a problem, so I really don't want to change them.

This is the light fixture: light fixture

This is the electrical box: electrical box

And here's the problem: screw hits wall of electrical box

Any help is appreciated.

Edit: I just tried a 4" round old work box (with the "flags") and it has the exact same problem... Is there a different type of box that I need to be using for this? How would you make this work in an "old work" style situation (E.g. I have a 3.5" hole in the center of my ceiling)?

  • Wouldn't a 4" round ceiling box solve your problem? – SteveSh Mar 20 at 1:34
  • Do those exist that can support weight? I only saw these 3 1/2" old work boxes... – GreatBlakes Mar 20 at 1:35
  • How do the holes line up if you rotate the bracket 90 degrees? Seems more likely not than so from this picture, bu pictures can mislead - the other holes in the outer rim projection of the box might just match these if the bracket was rotated... – Ecnerwal Mar 20 at 2:14
  • No matter how I orient the bracket, the diameter of the case is just too narrow. I actually just tried dry fitting into a the "flag" type 4" box and that actually has the same problem... I need a completely different style box... somehow. Never thought I'd be in over my head on something so simple. – GreatBlakes Mar 20 at 3:28
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Edit: Sorry, trim the screws

In electrical, screws are not sacrosanct. If one is too long, you simply trim it. That's why your stripper-crimper multi-tool has thread shears around the center pivot.

Wrong holes

This box has 2 sets of holes at 2 different spacings.

The inner (closer) set of holes sit on inward sticking nubs. Those are the ones you are trying to line up on.

The outer (farther) set of holes sit pretty much on the rim of the box. They are 90 degrees from the other holes. Try those.


The reason for the two spacings is the two sizes of steel octagon box (pictured).

  • The older, now largely obsolete 3-1/2" trade size (3-1/2" across corners, 3" across flats) had 2-3/4" screw spacing.
  • The current 4" trade size (4" across corners, 3-1/2" across flats) has 3-1/4" screw spacing.

enter image description here

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  • Thank you for the info, however even if I use the correct holes 90° from the one I was trying, the outer longer mounting screws are still at the same distance– as in, the diameter of the electrical box cavity doesn't change, so I still run into the same issue. I found a way to make a 4" old work "flag" box work, and I'm hoping that it's going to be able to hold 5lbs even though it isn't rated for it. – GreatBlakes Mar 20 at 15:48
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Use an Adjustable Cross Bar

enter image description here

Here is one from Home Depot

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Moved from my comment so I could add a picture.

Wouldn't a 4" round ceiling box solve your problem? Something like this:

enter image description here

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  • That would certainly work, but I need an old work box. Do old work boxes come in 4" circular sizes (that are made to support weight)? I could only find that 3 1/2" size at Home Depot. – GreatBlakes Mar 20 at 1:44
  • @GreatBlakes -- try your local electrical supply house – ThreePhaseEel Mar 20 at 2:59
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I installed led ceiling light on such ceiling mounts enter image description here

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