I need to mount a 2 gang dry lining backbox on a drywall. like this one Now, the hole in the wall is too long, so the clips won't grip (or rather, only one clip will grip where the other one would be too far from the drywall edge). For reasons beyond my control I can't move the box. Any suggestions?

  • Can you estimate how much smaller the hole would need to have been for the clips to work?
    – Stanwood
    Apr 14, 2018 at 11:06
  • I'd say roughly 1 cm (or 2/5 of an inch if I'm not mistaken)
    – vale.maio2
    Apr 14, 2018 at 11:11

1 Answer 1


I assume you used this box to avoid tearing up a bunch of drywall. So let’s try for a solution that avoids that.

Mount a piece of wood inside the wall along the edge of the opening and mount to this piece of wood.

The wood must be small enough to fit inside the existing hole. Once in you rotate it into place and then mount with drywall screws going through drywall and into the wood. If this area is exposed wall (not covered by a picture, a TV, or other furniture) you will want to patch the screw heads.

Mounting to the wood may require some more DIY finesse. With so little room to work you may find you need to modify the clip attachment and find some other means to attach on that side of the box. Like maybe snip off the clamp part so the hinged piece sits flat agains the wood and then drive a screw in horizontally.

HOWEVER, by the looks of things this is a box intended for main electrics? If there are high voltage (>50V) connections in this box it is a code violation to modify it. In particular, it may no longer be fire resistant after modification.

  • 2
    May I suggest that the proper screw to secure the wood piece through the drywall is a drywall screw and not a conventional wood screw. You may want to edit your answer to show this.
    – Michael Karas
    Apr 14, 2018 at 12:06
  • Thank you Stanwood, I'll try that as soon as I can. Can't do it immediately, but I'll keep this page in my bookmarks.
    – vale.maio2
    Apr 14, 2018 at 16:23
  • Modifying the box is a violation of NEC 110.3 unless instructions say to do it. Apr 14, 2018 at 18:27
  • Check to see what is the maximum thickness that the clamp can encompass. It was designed to clamp onto 1/2" drywall, but for patching puroses you need it open to 5/8" or 3/4" or even 1" thick wall material. Depending on the clamp opening, you should attach a backer of 1/4" or 3/8" plywood to the back of the wallboard and then adhere a small strip of drywall to fill out the opening to support the flange of the box. Apr 14, 2018 at 18:31
  • 1
    Good point @Harper , I wasn’t thinking of that. Modified my answer accordingly.
    – Stanwood
    Apr 14, 2018 at 18:41

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