What is the purpose of this type of metal faceplate?

How is it intended to be used?

metal faceplate

2 Answers 2


That mounts on a square steel electrical box and performs three functions:

  1. It provides mounting screw holes for two single-gang devices. Square steel boxes don’t come with device screw holes.
  2. It raises the device away from the box, so that when the box is mounted flush with the surface of a stud, the device will be flush with the surface of Sheetrock on the wall instead of sunken 1/2 into the wall as it would be if it weren’t raised.
  3. It allows the use of any (possibly decorative) cover plate over any devices you install (as opposed to domed cover plates are pre-stamped for specific device shapes only, and have an “industrial” look that isn’t suitable for many contexts).
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    4. It adds a little "volume" to the junction box for "box fill" purposes.
    – Huesmann
    Commented Jun 26, 2023 at 11:25
  • What I was most confused about was the gap in between the receptacles, if I used this faceplate just by itself. I guess it’s assumed you’ll attach a plastic faceplate over this?
    – Marco
    Commented Jun 28, 2023 at 2:39

That is for a standard 4x4 steel junction box. That is not a gang box, and has "proprietary" screws in the corners.

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Mud ring. Also available in 2-gang.

That cover is called a "Mud Ring". It's used when drywall will be going over the metal box. You install the box flush to the studs. You then install a "Mud Ring" of the thickness of the drywall. This creates a 1-gang or 2-gang opening which you then drywall up to, and you finish it normally with a 1-gang or 2-gang cover plate.

The mud ring provides access to the box interior. That means it never needs to be removed again, and can be covered with drywall panel and mudded in.

Grounding is handled same as any other metal box - ground is carried to the mud ring by its flush contact with the box.

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Domed cover. Available in a number of configurations, 1-gang and 2-gang.

If the box is surface-mounted, use a "Domed Cover". These work differently - the devices mount into the cover and then the cover bolts into the corner screws. This would never be mounted into drywall and mudded over, as it would then be impossible to get inside the box. So it's used when the back or front of the box is flush with the wall. This works better than mud rings and normal covers, because the normal cover would snag your clothes.

Note that the crushed corners carry grounding to the device, so a ground wire is not needed.

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