What type and size of screw should I use to mount a 4”x4” metal electrical box to the back of the under the sink cabinet?
Electrical Box – What Kind of Screw to Use for Mounting an Electrical Box Inside a Cabinet?
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Related Solutions
Most likely 8-32, possibly 6-32. Watch out, 8-32 is fine thread.
The -32 is intentional as it assures enough thread engagement.
Make sure you are hanging your fan by more than just a couple #8 screws!
The screw should not be larger than the factory drilled hole which looks to be 1/4". Typically seen in the field are #10 x 1" Slotted Hex Washer Head Sheet Metal Screw.
You can go longer than 1" but for that bar hanger probably not necessary.
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Best Answer
For box mounting I use 2 #8 pan/ washer head screws. All the ones I have seen are Phillips or square drive #2, but there may be straight. Inspectors like the square head #2 because usually only electricians use these so it can help you pass inspection. At least 3/4” but 1” is the max I normally buy because the next size is usually 1.5” and that’s too long, especially if no drywall (don’t want to drive a screw through a cable).