What Are The Standard Sizes For Set Screw Lighting?

The standard size of a set screw for lighting depends on the type of light fixture and the country. In the United States, the most common light bulb base size is the E26 or Medium/Standard, which is 26mm in diameter and used in most incandescent, vintage LED, CFL, and halogen smart light bulbs. The second most popular is the E12 or Candelabra, used for smaller decorative incandescent or nostalgic bulbs. In the early 1900s, the American standardization of lamp thread sizes enabled the mass production of lighting, with most table and bridge lamps assembled with 1/8 IP fittings and large reflector floor lamps and chandeliers using 1/4 IP fittings. Today, the size of a set screw for lighting can vary, with some fixtures using 8-32 screws, while others use 6-32 or 10-32 screws.

Screw sizes for imported lighting fixtures

Screw sizes for light fixtures can vary depending on the type of fixture, the size and weight, and the region you are in.

In the US, for example, the standard screw size for device boxes is 6-32, while junction boxes typically use 8-32 screws, and ground screws are 10-32. For light fixtures, 8-32 screws are often supplied, but these can be of poor quality and may not fit securely. Some fixtures may also use 10-32 screws.

For smaller fixtures, 6-32 screws are usually sufficient, while larger, heavier fixtures should use 8-32 screws. If you are hanging a ceiling fan, it is important to ensure the box is ceiling fan-rated and can support the weight. In this case, 8-32 or 10-32 screws are more suitable.

It is worth noting that some imported lighting fixtures may come with non-standard screw sizes, which can be frustrating to work with. In such cases, it may be necessary to use your own screws or tap the bar and ball nuts to fit the screws you have.

When working with light fixtures, it is always a good idea to have a variety of screw sizes on hand, such as 6-32, 8-32, and 10-32, to ensure you have the right size for the specific fixture and application.

Screw sizes for domestically-manufactured lighting fixtures

The screw sizes for domestically-manufactured lighting fixtures vary depending on the specific fixture and application. Here are some common screw sizes and their usage:

Edison Screw Base:

The most common type of light bulb base is the Edison screw base, found on incandescent, halogen, CFL, and LED bulbs. The size is denoted by a letter "E" followed by a number indicating the diameter in millimetres. Here are the common sizes:

• E12: Used for nightlight bulbs and ornamental bulbs in chandeliers and bathroom mirrors.
• E17: Used for desk lights and appliance bulbs, but less commonly available.
• E26: The standard size for most light bulbs in the United States.
• E39: Utilised for street lights and high-wattage lamps.

Metric Screws:

Metric screws are also commonly used in lighting fixtures. The size is denoted by a letter "M" followed by the diameter in millimetres. Here are some common sizes:

M3.5 or M4: These smaller metric screws may be used in certain lighting fixtures.

8-32 Screws:

8-32 screws are commonly supplied with light fixtures, but some professionals choose to use their own screws as the supplied ones can be wobbly and of lower quality. These screws are typically used for mounting the fixture's crosspiece into the junction box.

It's important to note that the screw size may vary depending on the specific lighting fixture and the type of electrical box being used (metal or plastic). Some professionals recommend using longer screws and adjusting the length as needed. Additionally, the quality of screws supplied with fixtures may vary, with some reporting issues with cheap, imported screws that don't conform to standard sizes.

Screw sizes for light bulbs

Screw-in light bulb fittings are named after their inventor, Thomas Edison, and are commonly known as Edison Screws or ES. The second part of the name corresponds to the diameter of the lamp holder that the bulb screws into. So, for example, an E12 screw fits into a 12mm holder, while an E17 screw fits into a 17mm diameter holder. The number measures the diameter of the lamp holder and not the size of the bulb's screw, as the screw cap on a bulb is slightly smaller than the fitting.

The most common light bulb base sizes are:

• Standard-Medium, a regular-sized screw-in base: E26 or E27
• Candelabra, a smaller screw-in base: E12
• Bi-pin, a pin-in base with two points of contact: G4 or GU24
• Twist-And-Lock base: GU10

The E26 or E27 Edison Screw is the standard 27mm diameter screw cap for 240V light bulbs in the UK and Europe. The E26 is the 26mm variant designed for the 120V market in the US.

The E12 base is also known as the "Miniature Edison Screw" (MES) and is used for nightlight bulbs, as well as decorative lightbulbs for chandeliers and bathroom mirrors.

The E14 is also known as the "Small Edison Screw" (SES) and is used for smaller decorative fittings, chandeliers, and appliance light bulbs. It has a diameter of 14mm and is predominantly used in the UK and Europe.

The E17, or "Intermediate Edison Screw" (IES), is used for desk lamps and appliance bulbs but is not very common.

The E39, or "Mogul", is used for street lights and high-wattage lamps.

Screw sizes for light fixtures

Standard Screw Sizes for Light Fixtures:

The most common screw sizes used for light fixtures are 6-32, 8-32, and 10-32. These screws are typically used for different components of the light fixture:

• 6-32 screws: These screws are commonly used for securing receptacles, switches, and cover plates to plastic boxes and steel mud rings. They are also used for attaching cover plates to miscellaneous devices like receptacles and switches.
• 8-32 screws: Octagonal fixture boxes, typically measuring 4" or 4-11/16", often use 8-32 screws. These screws are also commonly found in light fixtures and are used for screwing the crosspiece into the junction box.
• 10-32 screws: These screws are frequently used for light fixture brackets and ground screws.

It is worth noting that some light fixtures may come with cheaper, lower-quality screws that are prone to being too loose or wobbly. In such cases, it is recommended to use your own higher-quality screws for a more secure installation.

Edison Screw Base Sizes for Light Bulbs:

When it comes to light bulbs, the most common screw base type is the Edison screw base, which can be found on incandescent, halogen, compact fluorescent (CFL), and LED bulbs. The size of the Edison screw base is typically denoted by a letter "E" followed by a number indicating the diameter of the base in millimeters (mm):

• E12: Also known as the "Miniature Edison Screw" (MES) or "Candelabra" base, this size is used for nightlight bulbs and decorative light bulbs in chandeliers and bathroom mirrors.
• E17: The intermediate Edison screw base is less commonly found and is used in desk lights and appliance bulbs.
• E26: The medium or standard Edison screw base is the most common size in the United States, used for the majority of light bulbs.
• E39: This size, also known as the "Mogul" base, is utilized for street lights and high-wattage lamps.

Lamp Thread Sizes:

When working with antique or vintage lamps, it is important to understand the standard lamp thread sizes. Here are some common lamp thread sizes and their applications:

• 8-32: Used as holder screws for some glass shades.
• 1/4-20: This thread size has a 9/16" outside diameter.
• 1/4-27: Used on the tops of lamp harps and most lamp finials, with a 7/32" outside diameter.
• 1/8 IP-27: A very common lamp thread size with a 3/8" outside diameter, used with most lamp sockets, table lamps, and lamp finials with large openings.
• 1/4 IP-18: This thread size, with a 1/2" outside diameter, is used for floor lamps, ceiling fixtures, and floor lamp bases.

In summary, the screw sizes for light fixtures can vary depending on the specific fixture and its application. It is always a good idea to have a variety of screw sizes on hand when working with light fixtures to ensure a secure and proper installation.

Screw sizes for light fixture boxes

The standard screw used for light fixture boxes is #8-32. The length of the screw will depend on the number of layers of sheet rock or tiles. For instance, if you have double-layered sheet rock, you may need to purchase longer screws.

It's important to note that the gap between the device box and the light fixture cannot exceed 1/4". If the gap is larger, you must use an extension ring.

You should also be aware that you cannot use sheetrock screws for mounting light fixtures. This is because sheetrock screws have sharp edges that could cut into the insulation of the wires inside the electrical box, which may cause a short circuit.

If you are unsure about the screw size, you can use a drill bit to gauge the appropriate size. A #6-32 screw is .138 inches in diameter, while an #8-32 screw is .164 inches in diameter.

Frequently asked questions