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Light Bulb Base Sizes

Whether you are installing a bulb in your room, in some electrical appliance, any workshop projector of yours, your car, or anywhere else, you must be using the right bulb base and socket sizes.

This is to ensure that your bulb and its socket is compatible with the bulb base where you want to install a bulb. Although, since different applications require bulbs of different sizes, you should be familiar with all light bulb base sizes, which primarily includes the following ones.


Screw Bases

Whenever you talk about light bulbs, a screw base is one of the most common options you will find out there. Just per the name, a screw base bulb allows you to simply screw in a bulb via the threads present on the bulb as well as inside the socket.

Usually, screw base bulbs are used for ceiling lights, lamp lights, outdoor lights, and other general lighting applications around homes and offices. Although, not all screw bases are the same since they all have different diameters resulting in the following types of screw bases:

  • Miniature Screw E10: 10 mm diameter, ideal for miniature bulbs that might be used in flashlights and small appliances

Miniature Screw E10

  • Miniature Candelabra E11: 11 mm diameter, ideal for using in home appliances like fans, chandeliers, lamps, and others

Miniature Candelabra E11

  • Candelabra E12: 12 mm diameter, ideal for using with lamps and decorative lighting fixtures

Candelabra E12

  • European E14: 14 mm diameter, ideal for using in lamps and Christmas lights in countries like Europe and China

European E14

  • Intermediate E17: 17 mm diameter, ideal for small and compact bulbs that may be used in lamps and other decorative lighting options

Intermediate E17

  • Medium E26: 26 mm diameter, ideal for common sized bulbs used in European countries for home and office usage

Medium E26

  • European Medium E27: 27 mm diameter, ideal for similar usage to that of E26, including home and office lighting fixtures

European Medium E27

  • Mogul E39: 39 mm diameter, ideal for using with high power bulbs made for homes and offices in North American regions

Mogul E39

Fluorescent Pin Bases

If you are in the market to buy new light bulbs and other light fixtures, then you can find many kinds of bulb types. This includes options like LED lights, CFL lights, and even fluorescent tubes. And taking a look at the latter option of fluorescent tubes, this is exactly where fluorescent pin bases are used to install fluorescent tubes.

You can find fluorescent pin bases to be used in home lighting, industrial lighting, and even in many appliances where you would want proper lighting. But because different fluorescent tubes have different sizes in terms of length and diameter, they may use different fluorescent pin bases like these ones:

  • Miniature Bipin: ⅝ inch diameter, ideal for small-sized fluorescent tubes used in decorative purposes

Miniature Bipin

  • Medium Bipin: 1-inch diameter, ideal for commonly used fluorescent tubes used in homes and offices

Medium Bipin

  • Single Pin: ¾ inch diameter, ideal for large-sized fluorescent tubes made for industrial usage

Single Pin

  • Recessed Double Contact: 1-inch diameter, ideal for high power fluorescent tubes with safe installation

Recessed Double Contact

  • 4 Pin: 1 ⅛ inch diameter, ideal for circular fluorescent tube bulbs made for decorative purposes

4 Pin

  • Single-Ended 4 Pin: ⅝ inch, ideal for compact and miniature-sized fluorescent tubes used in appliances and electronics

Single-Ended 4 Pin

  • 2GX-13: ⅝ inch, ideal for circular and different shaped fluorescent tubes that are ideal for decoration and ambient lighting


  • Axial: 9/32 inch, ideal for compact and small-sized fluorescent tubes that might be used in small and tight spaces


Twist and Lock Bases

Even though you may consider twist and lock bases similar to screw bases stated above, they have a completely different design. Just per the name, these light bulbs not only twist to go in, but they also offer an inbuilt lock. This ensures that the bulb stays in place unless someone wants to take it out.

When installing a twist and lock base bulb, you have to simply insert the bulb into the base and then twist. But when you are about to reach the end of the twist, the bulb tightens up and locks for extra safety. Usually, you will find twist and lock bases to be used in small CFL and LED lights which primarily includes the following types of bases:

  • GU10: 10 mm diameter, ideal for ceiling-mounted lights and other decorative lights

  • GX10: 10 mm diameter, ideal for similar uses of GU10 with better installation and security


  • GU24: 24 mm diameter, ideal for large-sized bulbs with twist and lock bases with proper safety


Bayonet Bases

The bayonet base type made for light bulbs is another highly popular option out there. Its installation procedure is quite similar to those of screw bases and twist and lock bases. For installing a bayonet base, you have to first push in the bulb, followed by a twist motion.

With this, you get a proper lock for the bulb to ensure that it stays in place at all times. Talking about the common applications for bayonet bases, these are mostly used for ceiling and wall lights used in most homes and offices. But similar to other types of bulb bases, not all bayonet bases are the same since they differ from each other in terms of their size, as shown here:

  • Miniature Bayonet: 9 mm diameter, ideal for small emergency home lights and night lights

Miniature Bayonet

  • Double Contact Bayonet BA15d: 15 mm diameter, ideal for full-sized and high power light bulbs used in homes and offices

Double Contact Bayonet BA15d

  • Single Contact Bayonet BA15s: 15 mm diameter, ideal for common home bulbs with moderate power usage

Single Contact Bayonet BA15s

  • D. C. Bayonet Medium BY22D: 22 mm diameter, ideal for light bulbs that run on D.C power

Bayonet Medium BY22D

  • Index Double Contact Bayonet: 15 mm diameter, ideal for using with light bulbs where you want secure contact

Index Double Contact Bayonet

Additional Light Bulb Bases

While we have already stated most of the popular types of light bulb base sizes available out there, you can still find a few additional light bulb bases. This includes the base types which might not fall into a particular category but still get widely used. Hence, you should also consider the following light bulb bases while selecting the right one for your bulb type and lighting needs:

  • Bi-Pin Bases: 4 mm – 12 mm diameter, includes models like G4, G5, GY9, G12, used for small and miniature bulbs used in lamps and electronics

Bi-Pin Bases    Medium Bipin  Miniature Bipin

  • Wedge Bases: 5 mm – 8 mm diameter, includes models like wedge, wedge D.F, wedge S.F, slide, RX7s, used for vehicle lights and landscape lights with low wattage

Wedge Bases

  • Compact Fluorescent Plugs: 2 mm – 12 mm diameter, includes models like G23, G24, 2G7, used for decorative lighting and lamps with miniature fluorescent tubes


  • Miniature and Automotive Bases: 5 mm – 15 mm diameter, includes models like prefocus, straight, miniature single contact, used for cars and bike headlights and tail lights


  • Specialty Bases: 5 mm to 15 mm diameter, includes models like lead wires, contact lugs, screw terminal, side prong, used for highly specialized applications like circuits, electronics, appliances, and others


  • Cable Bases: includes models like male flat, female flat, PK30d, used for applications requiring flexible and long cable ended lights



With these various light bulb base types in your mind, you can choose the right type of bulb base as well as a bulb for your required applications. All of the light bulb base sizes have been stated above alongside their diameter and preferred applications. This should be helpful to easily understand their differences and pick the right one for you. If you have gone through all these different light bulb base sizes, make sure to share your thoughts in the comments section. You can also post any questions down there if you have any!

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