Choosing The Right Screws For Metal Junction Box Covers

metal junction box cover screw size

Metal junction box cover screw sizes vary depending on the type of box and its application. The most common screw sizes for metal junction boxes are 6-32, 8-32, and 10-32. The 6-32 screw size is commonly used for outlet screws and cover plates, while 8-32 is often used for light fixture screws and junction boxes that need to support more weight. The 10-32 screw size is typically used for ground screws and mounting heavy items like ceiling fans. It's important to use the correct screw size to ensure mechanical security and avoid damage to the threads.

Characteristics Values
Most common screw size 6-32
Other common screw sizes 8-32, 10-32, 10-24
Screw size for outlet screws 6-32
Screw size for light fixture screws 8-32
Screw size for junction boxes 8-32
Screw size for ground screws 10-32
Screw size for cover screws 6/32

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Screw sizes for metal and plastic boxes

When it comes to screw sizes for metal and plastic boxes, it's important to select the right type and size to ensure a secure fit and maintain the integrity of the electrical system. The specific screw size will depend on the application and the weight of the objects being attached. Here are some common scenarios and the recommended screw sizes for each:

Electrical Box Screw Sizes:

The most common electrical box screw size is a 6-32 machine screw. This size is suitable for both metal and plastic boxes. However, for heavier applications or when more strength is required, you may need to use an 8-32 or even a 10-32 screw. The thread pitch for all these screws is 32, which means there are 32 threads per inch on the screw shaft.

Outlet and Switch Screw Sizes:

Outlet screws are typically 6-32 machine screws, and the length can vary depending on the application. The most common length is 3/4 inch, but you can also find outlet screws ranging from 1/2 inch to 1 inch in length. For GFCI outlets, shorter screws, such as 5/16-inch, may be needed to accommodate tile walls.

Light Fixture Screw Sizes:

Light fixtures usually require a stronger screw due to their weight. The recommended screw size for light fixtures is an 8-32 machine screw, with a length of 2 inches or more to provide extra support and make installation easier.

Junction Box Screw Sizes:

Junction boxes often hold heavier objects, so they typically use a heavier-duty screw such as an 8-32. This screw size can provide more weight-bearing capacity and security for the attached fixtures.

Ground Screw Sizes:

Ground screws are larger and are typically 10-32 in size. They are generally 5/16 inches long, but longer screws can also be used. By convention, ground screws are painted green to indicate their function. Hex heads are commonly used on ground screws as they offer multiple driving options and are less likely to strip.

It's important to note that using the correct screw type and size is crucial for safety and maintaining the integrity of the electrical system. Always refer to the manufacturer's instructions or consult with a qualified electrician if you are unsure about the appropriate screw size for a specific application.

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Screws for mounting fixtures

When it comes to screws for mounting fixtures, there are a few different types and sizes that are typically used. The most common type of screw for this application is the machine thread screw, which comes in various sizes such as 6-32, 8-32, and 10-32. The specific size of screw you need will depend on the type of fixture and box you are working with.

For example, octagon/round junction boxes typically use 8-32 screws, while some weatherproof round boxes may use 10-24 screws. It's important to note that using screws with larger dimensions or alternative threading can cause cracking or breaking in moulded screw bosses in non-metallic outlet and device boxes. Additionally, substituting screws incorrectly can cause adverse effects on non-metallic boxes.

When purchasing screws for mounting fixtures, it's recommended to buy electrical box cover screws that are specifically designed for this purpose. These screws can be found at most hardware stores and are usually labelled as electrical box cover screws. They come in a variety of versions, including long/short, metal/plastic, and different finish colours.

It's also worth mentioning that some fixtures, such as light fixtures, may come with their own screws. However, these screws are often of lower quality and may not provide a secure fit. As such, it's generally recommended to use your own screws that are more snug and provide better peace of mind.

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Screws for switches

When it comes to screws for switches, there are a few different types and sizes that you may need, depending on the specific application.

Types of Screws

Firstly, it's important to note that screws for switches typically have either a flat, round oval, or pan head. They can also be Phillips, slotted, combination, or tamper-proof. Additionally, some screws are self-tapping, meaning they can tap their own hole as they are driven in, eliminating the need to pre-drill a hole.

Sizes of Screws

The most common size of screw for a switch plate is 6-32, which corresponds to a thread diameter of #6 and 32 threads per inch. The specific length of the screw will depend on the device you are covering and the type of mounting plate being used. For example, a 5/16" screw length is typically used for rocker, Despard, and vintage low voltage switch plates with strap mount plates, while a 1/2" screw length is used for toggle, duplex, blank, and simplex switch plates with box or device mount plates.

For octagon and round junction boxes, an 8-32 screw size is often required. However, some weatherproof round boxes may use a 10-24 screw size.

It's worth noting that the National Electrical Code (NEC) specifies the minimum screw size for fixture support in octagon boxes as 8-32. Additionally, the National Electrical Code (NEC) requires a -32 thread or finer for grounding screws in standard steel junction boxes to ensure secure thread engagement and proper electrical grounding.

When choosing the right screw for your switch, it's important to consider the compatibility of the screw size and threads with the threaded holes in the junction box. Using screws with larger dimensions or alternative threading can lead to cracking or breaking of the screw bosses in non-metallic outlet and device boxes.

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Screws for cover plates

When it comes to screws for cover plates, there are a few standard sizes that are typically used. The most common sizes are 6-32 and 8-32, although you may also come across 10-32 or 10-24 screws. These screws are usually available in a range of lengths, from 3/8" to 1" or longer, to accommodate different types of cover plates and devices.

For example, if you have a cover plate that attaches to the strap of your electrical device, such as a rocker-shaped device like a Decora rocker switch or a GFCI outlet, you'll need shorter 5/16" screws. This is to prevent the screws from hitting the wall before they're fully tightened. On the other hand, if you have a plate with screw positioning that aligns with the electrical box's tabs, you can use standard 1/2" screws. This includes blank electrical box covers, phone jack covers, and coax cable jack plates.

When choosing screws for cover plates, it's important to consider the compatibility of the size and threads of the screw with the threaded holes in the box. For example, sheet steel metallic boxes designed according to NEMA OS1 require screws with 32 threads per inch. Using the wrong size screws can lead to cracking or breaking of the screw bosses in non-metallic outlet and device boxes.

You can typically find cover plate screws at hardware stores or online retailers, and they are often available in a variety of materials, including metal and plastic, and different colours to match your cover plates.

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Screw heads and types

Screws are manufactured with different head styles, each serving a unique functional or decorative purpose. Understanding the differences will help you decide which style to choose for your project.

Countersunk vs Non-Countersunk

There are two basic screw head designs: countersunk and non-countersunk. Non-countersunk heads are fully exposed and include binding, button, cheese, fillister, flange, hex, pan, round, socket and low socket, square, and truss heads. Countersunk designs include flat, oval, and bugle heads, which require a countersunk hole unless the material is very soft. Flat and oval heads are often used in finish work and can be hidden with a screw cover for a cleaner look. Bugle heads are commonly found in drywall screws and automatically create their own countersunk hole during installation.

Drive Styles

The drive style or drive recess refers to the type of tool needed to install or remove a screw. Common drive styles include slotted, Phillips, combination, hex, hex socket, square, Torx®, and spanner. Slotted and Phillips screwdrivers are versatile and can be used with metric screws, while metric hex keys are required for metric hex socket screws. Phillips, square, hex, and Torx® drive screws are also popular as there is less chance of the driver slipping out and scratching the finish.

Selecting the Right Screw Head

Choosing the appropriate screw head is essential for ensuring a secure fit and preventing damage to materials or tools. For example, flat head screws are popular for their versatility and clean, low-profile finish, making them ideal for aesthetics-driven projects. On the other hand, Phillips head screws allow for greater torque and are widely used in household repairs and industrial applications. Torx head screws are designed to prevent cam-out and provide a superior grip, making them a preferred choice for automotive and electronic repairs. Hex head screws, with their six-sided design, excel in situations requiring brute strength and durability, such as construction and machinery.

Specialty Screw Heads

Specialty screw head types are designed for specific industries or unique applications. For instance, the electronics industry relies on tiny pointed tip screws with a low profile to fit into tight spaces. In contrast, the construction industry may require screw types capable of handling high torque and providing a secure hold in materials like concrete. Understanding the unique advantages of specialty screws can greatly enhance the efficiency and outcome of your projects.

Frequently asked questions

The standard screw size is typically either 6-32 or 8-32.

Yes, 10-32 screws are sometimes used, especially for weatherproof boxes.

The diameter of a 6-32 screw is 0.138 inches or 9/64 inches.

It is recommended to use round-head or hex-head screws inside the box to prevent arcing and oval-head screws for attaching cover plates.

The length of the screw will depend on the application. For cover plates, 5/16" or 1/2" screws are commonly used.

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