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Light Bulb Fitting Finder (Caps and Bases)

September 26, 2012   

Some confusion can arises when referring to ‘fittings’. A light fitting is the ‘socket’ into which the light bulb is installed. However, many people speak of the ‘fitting’ on the lamp itself, referring to the part of the lamp that secures it into it’s holder. This is the ‘cap’ or ‘base’ and both holds the lamp in position and provides the connection to the power supply.

There are a large number of different fitting options available in modern lighting, so this section is designed to help you identify the fitting that you requrie to ensure that your new lamps easily replace existing ones. To keep things concise we have only included the most popular fittings in this guide. However, we do stock numerous specialist lamps, so if you are unsure then just give us a call.


GU10The most popular type of lamp that we sell at YourWelcome is the GU10. Most downlighter fittings use either the 240v GU10, as shown on the right, or the low voltage equivalent, the MR16 fitting which differs slightly as detailed below.

The GU10 cap/base features two bayonet style pins, which require a push into the socket, followed by a twist to lock in position. These are sometimes referred to as ‘Twist and Lock’. We sell GU10 lamps in a variety of forms, including the common halogen 50w and 35w available in GU10 Halogen and the ultra low energy and long life LED versions available in GU10 LED.



Our second most popular lamp is the MR16. These lamps are of a similar size and application to the GU10, but are low voltage so run off 12v rather than 220-240v and therefore employ a different fitting and base. Rather than the Twist and Lock of the GU10, the use two pins which are pushed into two corresponding holes on the lamp holder. These bases are often referred to as GU5.3

They are available in both Halogen and LED forms to suit individual requirements. View our range of LED MR16 bulbs.

Bayonet Cap (BC)

Bayonet Cap (BC)The standard bayonet cap (BC) fitting will be a familiar sight to most, as most traditional lightbulbs used either this or the Edison Screw (ES) shown below. The BC cap is installed with a simple ‘Twist and Lock’.

The ‘Small Bayonet Cap’ or SBC is also common and is shown below. We no longer stock traditional lightbulbs that use this fitting, but instead offer various Low Energy replacements in spiral and candle form.

Small Bayonet Cap (SBC)

Small Bayonet Cap (SBC)The Small Bayonet Cap (SBC) is identical to the BC, just smaller in size. It is designed for more compact bulbs and smaller fittings and it is fitted in the same way as the larger version. These are commonly used in lower output situations such as bedside lamps.

Edison Screw Cap (ES)

Edison Screw Cap (ES)The Edison Screw (ES) cap is another ‘traditional’ light base, differing from the BC simply by a screw fitting rather than Twist and Lock.

A Small Edision Screw (SES) is also common and is simply the a smaller version of the ES. It is shown below. As with the BC, we do not stock the outdated traditional bulbs that originally used the ES, but offer several Low Energy alternatives.

Small Edision Screw (SES)

Small Edision Screw (SES)The Small Edison Screw (SES) is simply a smaller version of the ES for more compact lamps and fittings. These are often found in fixtures such as bedside lamps that do not require a lot of light output.

Halogen Capsules – G9

Halogen Capsules - G9The G9 Halogen capsule uses two looped pins at the base and is simply pushed into the fitting to install.

Unlike other capsules in our range it is designed for 220-240v mains use and is available in several different power options, depending on the light output required. View our range of G9 light bulbs.

Halogen Capsules – G4

Halogen Capsules - G4

The G4 is a low voltage capsule lamp that uses two pins spaced 4mm apart. The pins differ from the G9 as they are straight without the wire loop. They are simply pushed into the fitting to install.

Like the G9 they are available in a range of power options to tailor to your needs. View our range of G4 light bulbs.

Jason Harvey
February 6, 2015 at 11:38 am

Do I need to use a fully enclosed light fitting for 240V LED downlights under a flat roof. There is supposed to be 150 mm of insulation above my plaster board in this room. If I have to cut most of that away to fit the downlights then I’m not going to have a very warm room.

February 7, 2015 at 1:16 pm

Hi Jason, You don’t have to fit enclosed fittings, these are normally fire rated to stop the spread of fire through the roof void. You can leave air space around the fitting and lamp, fit a fire shroud, available from B&Q etc.. if you want to. If you are installing LED lamps, which you can purchase from,, they generate very little heat and do not need much air space, between insulation and joists or floor. Any other questions please ask.


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