Last night I was try to put up a shelf across this narrow wall protrusion in my semi-finished garage. Magnetic stud finder registered on the edges but not in the center of the wall, so I believed it was a standard wood framed in piece of drywall. When I started drilling pilot holes I made it about 1/16" into the plaster before I hit something metal. Same on the other side. What could this be? It's garage level. I can't think of any reason why there would be a ventilation duct there, or why someone would skim coat a duct anyway.

  1. what could this be?
  2. can I still into it for my shelves, which I already cut to exactly the width of this wall?

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  • is there anything below the garage? Commented Feb 5, 2021 at 14:25
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    I can't think of much reason for a "wall protrusion" like that other than a duct. As in, if you showed the me the second picture and not the first, I'd say "looks like duct must be here."
    – Ecnerwal
    Commented Feb 5, 2021 at 14:40
  • Is your furnace on the other side of that wall? Having plenums in garage spaces is common.
    – Ed Beal
    Commented Feb 5, 2021 at 14:42
  • It looks like you've drilled a fair bit into the metal indicating that it's got some thickness. Duct work is generally pretty thin stuff. However, metal plates to protect wiring & plumbing are fairly thick for exactly this reason. You've got electrical in conduit next to the chase, so it's likely not electrical, but there could be plumbing behind there. That would be an odd location for it, TBH (especially considering the exposed plumbing above). Can you tell how far into the metal you actually went?
    – FreeMan
    Commented Feb 5, 2021 at 14:47
  • 1
    This isn't a hollow wall, it's an enclosure. There must be something inside that protrusion. If it were mine I'd want to know what's inside. Just out of curiosity, never mind before drilling into it. Find a point with no stud or metal or anything, drill carefully through the drywall, and either saw open a hole so you can see what's inside or buy a cheap endoscope on Amazon to peek inside the enclosure. It's a garage, you can patch it up after and paint "one day". After that you can drill with confidence into something suitably strong for your shelves.
    – jay613
    Commented Feb 5, 2021 at 17:40

3 Answers 3


Turns out when you buy a $50 borescope you get what you pay for...but here's what I found inside the wall. Basically it seems to be a large plastic pipe, maybe waste. Towards the top, it bends towards the interior of the garage, and I expect whoever built this wall figured it was simpler to just frame the whole thing in to the depth at the top rather than do it on an angle (it is a garage after all). The corner appears to have a 2x4 stud, although it's hard to tell if it's exactly in the corner. Still, I don't see anything electrical or plumbing in the area so I'm going to put my money on "corner bead" and drill through. Thanks everyone.

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  • 1
    Thanks for coming back to answer your own question! Please be sure to give yourself a check mark once the system will let you.
    – FreeMan
    Commented Feb 10, 2021 at 13:23

Judging by the thickness and location of the metal you detected it seems like you might have metal drywall corner bead, which is typically installed on the edges of drywall to reinforce the area and prevent chipping.

Assuming that is what you found, the corner bead shouldn't interfere with the installation of shelves. That doesn't mean there isn't anything else behind the drywall that the stud detector isn't picking up, so proceed with care.

  • Generally, I'd agree with you, however that does seem a bit far in from the corner to still be hitting the corner bead. Of course, with no dimensions given, that's just a guess, but it doesn't seem right.
    – FreeMan
    Commented Feb 5, 2021 at 14:44
  • If you are within 1.5" of the edge id agree with CJC.... Your picture looks to be about an inch.
    – mark f
    Commented Feb 5, 2021 at 15:51
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    I put it at 1-1/8", and I agree. :)
    – isherwood
    Commented Feb 5, 2021 at 19:10
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    Just measured, and the pilot hole I was trying to drill is 3/4" away from the corner. (That protrusion is smaller than it looks, just ~14" across.) Are corner beads typically spackled over? Perhaps some more evidence: I tried drilling a hole in the center of the protrusion and it went through the drywall easily (no metal). And I tried another hole close to the corner about 4' down, and hit metal. So it definitely seems to be something related to the corner.
    – Aaron
    Commented Feb 5, 2021 at 19:41
  • I was drilling pilot holes into the studs for deck screws. Overkill? Figured it would hold better if drilled.
    – Aaron
    Commented Feb 7, 2021 at 3:22

It may be a nail plate

The job of a "nail plate" is to be a warning to craftsmen that a wire or pipe is close to the surface here.

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If you wish to stick holes in buildings, it is your job to know that, and to know what to do about it (i.e. stop, and either move, or do do more reconnaissance before proceeding; great time for a borescope).

A nail plate will stop nails, and is likely to stop drywall screws. But drills? Can't stop em. Any common bottom-shelf carbon steel drill bit is made for drilling steel and I drill steel with them all the time. So it is entirely up to you to notice the drill working harder, and stop.

  • 1
    Agreed, but that's an odd place for one...
    – FreeMan
    Commented Feb 5, 2021 at 19:13
  • Ordered an inexpensive borescope. As @jay613 said above, probably good to know what's in there anyway.
    – Aaron
    Commented Feb 5, 2021 at 19:46

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