The mounting holes in a device (switch) box are tapped for which screws?

• A. No. 4-40
• B. No. 6-32
• C. No. 8-32
• D. No. 10-32

Answer: (B)

The mounting holes in a standard device (switch) box are threaded to take machine screws of size 6-32. The “6-32” means a #6 diameter screw with 32 threads per inch, which fits the tapped holes in typical metal boxes and device yokes. This size provides the right balance of strength and fit, giving secure attachment without stripping the threads. Other sizes (smaller or larger) either won’t engage properly or won’t align with the box’s tapped holes, which is why they aren’t used for mounting switches to standard boxes.