Light Bulb Base or Socket Sizes Explained – A Complete Guide

This article presents a list of the available light bulb base or socket types and standard light bulb base sizes. Also covers, what do the different lamp bases mean, why different lamp bases are used for different lighting applications, and where those light bulb bases are used. Details are after the Light Bulb Bases chart or Socket Sizes chart image.

Light Bulb Socket Sizes chart

Light Bulb Base Sizes
Light Bulb Base Types and Sizes

Types of light bulb bases

SCREW BASES

  1. Miniature Screw (E10)
  2. Miniature Candelabra (E11)
  3. Candelabra (E12)
  4. European (E14)
  5. Intermediate (E17)
  6. Medium (E26)
  7. Mogul (E39)

E10 Base or Miniature Screw Base

In the lamp base designation “E-10” (sometimes called Miniature Edison Screw (MES), “E” stands for “Edison” and “10” indicates the diameter in millimeters as measured across the peaks of the thread on the base, e.g., E-10 base bulbs have a diameter of 10 mm. E-10 base light bulbs have a single contact on the bottom and are used in flashlights, indicators, and toys.

E11 Base or Miniature Candelabra Base

E11 (mini candelabra) is 11mm (0.433 in) in diameter and is a bit smaller than E12 (candelabra) which is 12mm in diameter. Its applications are very limited. E11’s are most commonly used for small, halogen (hot!) bulbs. Another most obvious application is obviously for 120-volt chandelier/candelabra. Low voltage models are used on Lionel toy trains and other toys. The E11 base is sometimes used for 50/75/100-watt halogen lamps in North America, where it is called the “mini-can”.

E11 Mini Candelabra Base Identification

E12 Base or Candelabra Base

As the name suggests, the fitting is 12 millimeters in diameter size and is often deemed the Candelabra Edison Screw (CES). It is the home of C7-sized lamps, so if you bought a C7 lamp before, it utilized the E12 fitting.

Bulbs with E12 bases are commonly used for decorative applications, such as chandeliers, wall sconces, Christmas lights, restaurant pendant lights, ornamental lights, residential or commercial string lights, and night lights. Many bulbs with these bases are designed to mimic the look of a candle flame.

Common bulbs with E12 bases:

  • Small tube-shaped bulbs: T8, T6, T22
  • Candle-flame-shaped bulbs: C7, C9, CA10, B10
  • Small globe-shaped bulbs: G14, G16, G50

E14 Base or European Base

European Or SES (Small Edison Screw) is a very common size used throughout Europe and the UK. An E14 bulb is one of the most-used bulbs in our homes found in many types of small light fittings around the home from bedside table lamps to wall lights and chandeliers . It is also called the bulb with the small screw socket. The bulb is called E14 because it refers to the socket: 14-millimeter diameter.

Common bulbs with E14 bases:

  • A-shaped bulbs: A15
  • Small tube-shaped bulbs: T8, T6, T22
  • Candle-flame-shaped bulbs: C7, C9, CA10, B10
  • Small globe-shaped bulbs: G14, G16, G50
  • Marquee and sign bulbs: S11

E17 Base or Intermediate Edison Screw Base

Intermediate Screw Base (E17) Bulbs are sometimes called Intermediate Edison Screw (IES), “E” stands for “Edison” and “17” indicates the diameter in millimeters as measured across the peaks of the thread on the base

Like candelabra bulbs with E12 bases, bulbs with E17 bases are used for decorative applications, such as chandeliers, wall sconces, Christmas lights, restaurant pendant lights, ornamental lights, and sign or marquee lights. Bulbs with these bases are commonly used for appliance lights, such as microwave lights, refrigerator lights, and range hood lights. They’re also found in ceiling fan light fixtures.

Common bulbs with E17 bases:

  • A-shaped bulbs: A15
  • Small tube-shaped bulbs: T8, T6, T22
  • Candle-flame-shaped bulbs: C7, C9, CA10, B10
  • Small globe-shaped bulbs: G14, G16, G50
  • Marquee and sign bulbs: S11

E26 Base or Medium Edison Screw (MES) Base

E26 is the size of most light bulbs used in the U.S. It’s referred to as having a “medium” or “standard” base.

The letter “E” in E26 refers to Edison Screw, the most standard of lamp bases, while the numerical “26” refers to its diameter in millimeters (approximately 1 inch).

E26 is also commonly referred to as a Medium Edison Screw (MES).

They are commonly used for general lighting in standard light fixtures, such as ceiling lights, lamps, can lights, outdoor spotlight and flood light fixtures, and vanity lights.

Common bulbs with E26/E27 bases:

  • A-shaped bulbs: A19, A15, A21
  • Globe-shaped bulbs: G30, G25, G16.5
  • PAR (parabolic aluminized reflector) spotlight and floodlight bulbs: PAR16, PAR20, PAR30, PAR38
  • BR (bulged reflector) spotlight and floodlight bulbs: BR20, BR30, BR40

E39 Base or Mogul Base

E39 is known as the large base or mogul base. Its typically what is used on older metal halides and high pressure sodium from 100 watts and up. The E is for Edison screw base and the 39 is 39 mm across. Larger than the standard E26 or 26 mm across.

The large E39 “mogul” base is used on street lights, and high-wattage lamps (such as a 100/200/300 Watt three-way). Chances are you won’t have a need for these guys.

Common bulbs with E39/E40 bases:

  • PAR (parabolic aluminized reflector) bulbs: PAR20, PAR38, PAR40
  • Blown tubular bulbs: BT37, BT56
  • Elliptical dome bulbs: ED17, ED28, ED37

FLUORESCENT PIN BASES

  • Miniature Bi-Pin
  • Medium Bi-Pin
  • Single Pin
  • Recessed Double Contact
  • 4-Pin
  • Single-Ended, 4-Pin
  • 2GX-13
  • Axial

Miniature Bi-Pin

Miniature BiPin, also called mini-BiPin, sockets have pins placed closer together. Not only are they smaller in size, but they’re also used in a smaller type of light too.

The miniature bi-pin sockets are used in linear fluorescent lighting, like T5 lights.

Medium Bi-Pin

When you’re wondering what the difference between a medium and a miniature bi-pin socket is, it doesn’t just involve the size of the part itself. The actual socket is what helps to generate the correct amount of electricity to the light. If the bi-pin is too small or large for the light, it could cause a significant electrical problem.

Medium bi-pin sockets are generally used in a variety of linear fluorescent bulbs, like the T8 and T10 lights.

Single Pin

Some linear fluorescents have a single pin Fa8, but they are not very common.

Recessed Double Contact

Some linear fluorescents have double contact R17d, but they are not very common.

TWIST & LOCK BASES

  • GU10
  • GX10
  • GU24

BI PIN BASES

A bipin or bi-pin (sometimes referred to as two-pin, bipin cap or bipin socket) is a type of lamp fitting. They are included in the IEC standard “IEC 60061 Lamp caps and holders together with gauges for the control of interchangeability and safety”. They are used on many small incandescent light bulbs (especially halogen lamps), and for starters on some types of fluorescent lights.

The bi-pin base was invented by Reginald Fessenden for the 1893 World’s Fair in Chicago.

  • G4
  • GU4
  • GZ4
  • G5.3
  • G5
  • GU5.3
  • GX5.3
  • GY5.3
  • G6.35
  • GY6.35
  • GZ6.35
  • GY8
  • G8.5
  • G9
  • G9 Pin Blade
  • G9.5
  • GX9.5
  • GZ9.5
  • G12

BAYONET BASES

  • Miniature Bayonet
  • Double Contact Bayonet (BA15d)
  • Single Contact Bayonet (BA15s)
  • D. C. Bayonet, Medium (BY22D)
  • Index Double Contact Bayonet

WEDGE BASES

  • Wedge
  • Wedge D.F.
  • Wedge S.F.
  • RX7s
  • Slide
  • Wedge Subminiature

COMPACT FLUORESCENT PLUG IN BASES

  • 2G7
  • 2GX-7
  • 2G11
  • G23
  • G24d-2
  • G24d-3
  • G24q-1
  • G24q-2
  • G24q-3
  • GX23
  • GX23-2
  • GX24q-1
  • GX24q-2
  • GX24q-3
  • GX24q-4
  • GX24q-5

MINIATURE & AUTOMOTIVE BASES

  • Prefocus
  • Right Angle Prefocus
  • Axial Prefocus
  • Straight
  • Midget Flanged Single Contact
  • Miniature Flanged Single Contact
  • Miniature Single Contact
  • P15S
  • P28S
  • P32d2
  • P43T
  • P43T-38
  • PK22s
  • PX26d

SPECIALTY BASES

  • G53
  • Festoon
  • 2 Contact Lugs
  • 3 Contact Lugs
  • Screw Terminal (Multi-Purpose)
  • Mogul End Prong (GX16d)
  • Metal Clip
  • Rigid Loop
  • Side Prong
  • Lead wires
  • S14s

CABLE BASES

  • MALE FLAT
  • FEMALE FLAT
  • PK30d

MISCELLANEOUS BASES

  • GU6.5