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I recently bought a new fixture for my back patio light. (Just replacing an old halogen motion-detector light with a new LED motion-detector light.)

Unfortunately, the mounting bracket for the new light has screw holes which are 3 1/2" apart, while the existing junction box has screw holes which are 2 3/4" apart. (And I can't use the old mounting bracket with the new light, because the way it attaches to the light is completely different.)

First off, is it the new light which is unusual for expecting 3 1/2", or is it the house that's unusual for having 2 3/4" holes?

How does one normally solve this problem?

Is it possible to buy a light fixture that works with 2 3/4" mounting holes? Unfortunately, none of the fixtures I can find online or in the store say what distance of mounting holes they expect... it isn't until you open the box that it says what it's expecting.

junction box with new mounting bracket

  • See this question and answer. – bib Aug 2 '17 at 22:24
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    And this one – bib Aug 2 '17 at 22:25
  • I don't think the crossbar would work, because the mounting bracket needs to have a threaded screw hole in the middle of it. That's how the new fixture attaches to the mounting bracket. – user31708 Aug 2 '17 at 23:30
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    There appears to be a 2 3/4 inch hole already drilled in your bracket. If it's not big enough for the screw, drill it out. The threaded mounting hole doesn't need to be in the center. The light housing will still cover everything. – Chris Cudmore Aug 3 '17 at 13:14
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Normally, we just take a drill and make a hole in the strap that lines up with the other hole.

2 3/4" would be an old bastard size so if your house uses these you may have this problem again.

Good luck!

  • Wow. The house was built in 1996. So they are only making light fixtures for houses less than 20 years old? – user31708 Aug 2 '17 at 23:32
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    Hmmm yeah in 30+ years, I haven't actually seen any of those used at all so I errantly assumed they were older than that. As you learned though, it is not a normal size that light fixture manufacturers plan for. It looks like they used a plaster ring on a 3" box hence the very small opening. Normally, contractors use a plaster ring on a 4" box giving you the 3 1\2" opening. Someone was trying to save some money with smaller boxes. – ArchonOSX Aug 3 '17 at 8:14
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The 2 3/4" and 3 1/2" sizes are both common. Many fixtures have screw slots for both.

A cross strap is a common way to adapt the larger size down to the smaller size. Screws to 3 1/2 box and 2 3/4 fixture mounts to strap bracket.

Some 2 3/4" boxes, particularly the metal styles, can allow a strap bracket to be mounted to the box and let the ends overhang the box so that screws on 3 1/2" centers can clear the outside of the box. In this case you can drill or open some holes under the bracket to allow the fixture mounting screws to go through the bracket and into the wall/ceiling.

You may want to also investigate the possibility to see if you can drill 2 3/4 mounting space holes in the fixture itself and forgo the use of any strap bracket itself.

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