Lamp Base Finder

The bottom part of the bulb or lamp that connects it into the light fitting is generally known as the ‘cap’ or ‘base’. There are a vast vanety of caps and bases and so our 'Base Finder' page has been created in order to help make sure that you choose the correct type of lamp.


The familier ‘bayonet cap’ base is also known as BC or B22 and used on most regular light bulbs. It has a 22mm diameter with two locating lugs.

The ‘small bayonet cap’ also known as SBC or B15 is similar but measures only 15mm across. It is generally used for mains voltage lamps, the SBC fitting can also be found in a very small number of specialist low voltage halogen lamps.

The Edison Screw or ‘ES’ lamp fitting is used universally. The most popular ES or E27 fitting is 27mm diameter and is widely used in both the US and Europe. For smaller fittings, the SES is used commonly in the UK and Europe.

Miniature halogen/LEDs capsule lamps are generally designated by the measurement in millimetres between the pins (e.g. the G9 has pins 9mm apart).

The G4 is always used in low voltage appliances, the G9 is for 240v mains use.


The most commonly used halogen spots are either the ‘push fit’ GU4 and GU5.3 low voltage type or ‘twist and lock’ GU10 and GZ10 mains versions.

Compact fluorescent/LEDs lamps (CFLs) without integrated control gear generally use ‘push-fit’ square or rectangular fittings. Those with integral starters use 2-pin fittings. For those for use with electronic control gear and/or dimmers will have 4-pin connectors