Dimensions of fastener strips for household electrical distribution boxes

The standard fasteners for household electrical boxes are typically #6-32 machine screws, with lengths ranging from 1/2 inch to 1-1/2 inches, while metric screws like M3, M4, M5, and M6 are also commonly used in distribution boxes.

Standard Screw Sizes

For North American household electrical boxes:

• Device mounting screws (for switches and outlets) are usually #6-32 machine screws, with a diameter of 0.138 inches and 32 threads per inch (TPI) for secure engagement .
• Lengths vary depending on the application: 1 inch is standard for most outlets and switches, 1-1/2 inches for recessed installations, and 5/16 inch for cover plates .
• Head types are typically flat-head Phillips or slotted for devices, and oval-head for cover plates . For distribution boxes and circuit boards, especially in metric systems:
• Common metric screw sizes include M3, M4, M5, M6, and M8, with M3 and M4 used for smaller components and M5–M8 for medium to larger parts .
• Materials vary: brass screws are corrosion-resistant and electrically conductive, stainless steel screws offer chemical resistance, and alloy steel screws provide higher strength .
• Head types include pan head, button head, and hex drive, depending on the application and aesthetic requirements .

Fastener Strip Considerations

• Number of screws: Standard electrical boxes often use 8 screws for mounting, junction boxes 6 screws, and surface mount boxes 4 screws .
• Thread engagement: Fine threads (like 32 TPI for #6-32) ensure a secure connection resistant to vibration .
• Length selection: Must be sufficient to fully engage the device yoke without bottoming out, ensuring stability and flush installation .

Summary

For typical household electrical distribution boxes, #6-32 screws are the standard for outlets and switches, with lengths from 1/2 inch to 1-1/2 inches, while metric screws (M3–M8) are used for internal components and distribution box assemblies. Choosing the correct screw type, length, and material ensures safe, stable, and code-compliant installations .