What is the maximum gap allowed between drywall and the edge of a device box or plaster ring?

• A. 6 mm (1/4 in)
• B. 3 mm (1/8 in)
• C. 1 mm (1/16 in)
• D. 5 mm (3/16 in)

Answer: (B)

When you install a device box in drywall, the amount of space between the drywall edge and the box needs to be small enough so finish materials can bridge it and the device face sits properly with the wall surface. The limit is three millimeters (one-eighth of an inch). This keeps finishing compounds, mud rings, or plaster rings able to cover the gap cleanly, ensures the device is mounted flush, and prevents unsightly or unstable gaps after finishing. A gap larger than this would be hard to conceal and could lead to cracking or misalignment, while a gap much smaller would be difficult to accommodate finishing materials.