Light Bulb Base Types: How to Identify Your Fitting
Not sure which bulb fitting your light takes? Here are the six common base types — with what each looks like, its size and voltage, and how to tell them apart.
E27
ES · Edison Screw
- Fitting27 mm screw
- Voltage230V mains
- ConnectsScrews in
- Common inPendants, lamps
E14
SES · Small Edison Screw
- Fitting14 mm screw
- Voltage230V mains
- ConnectsScrews in
- Common inChandeliers, candles
B22
BC · Bayonet Cap
- Fitting22 mm, 2 side pins
- Voltage230V mains
- ConnectsPush & twist
- Common inOlder UK fittings
GU10
Twist-lock spotlight
- Fitting2 stubby pins, 10 mm
- Voltage230V mains
- ConnectsPush & twist ¼
- Common inRecessed spots, track
GU5.3
MR16 · 12V spotlight
- Fitting2 thin pins, 5.3 mm
- Voltage12V (needs driver)
- ConnectsPush straight in
- Common inLow-voltage downlights
G9
Capsule
- Fitting2 looped pins, 9 mm
- Voltage230V mains
- ConnectsPush straight in
- Common inWall lights, some chandeliers
How to identify your fitting
- Switch off and let the old bulb cool, then remove it.
- Look at the base: a spiral thread means a screw fitting (E27 or E14 — E27 is the wider one).
- Two pins means a pin fitting. Stubby pins that push-and-twist are GU10; thin straight pins are GU5.3; looped wire pins are G9; side pins on a smooth cap are B22 bayonet.
- Still unsure? The base code is often printed on the old bulb or the fixture, or measure across the screw / between the pins in millimetres.
Got your base? Now get the full bulb spec (brightness, colour, dimmable) with our Bulb Finder, or read Lumens, Watts & Kelvin Explained. We craft the fixtures, not the bulbs — any matching brand will fit.