The mounting holes in an outlet box are tapped for which screws?

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

Answer: (B)

The mounting holes in an outlet box are threaded to accept machine screws that fasten the device (receptacle or switch) to the box. The standard screw size for these holes is No. 8 with 32 threads per inch (8-32). Using 8-32 screws provides a secure, reliable connection that fits the typical device mounting ears and keeps the device properly aligned with the cover plate. Other thread sizes aren’t the common standard for this purpose in residential boxes, which is why 8-32 is the correct choice.