Last updated: 19 August 2026
B22 vs E27 fittings
E27 (screw) and B22 (bayonet) are the two bulb fittings most people run into. E27 is the international screw standard, used almost everywhere in the world, while B22 bayonet is the traditional fitting across the UK, Ireland, Australia, New Zealand, India, South Africa and other countries. They look similar at a glance but connect in completely different ways — and they are not interchangeable, so it pays to know which you have before you buy.
The two fittings
B22 (bayonet cap) has two small pins sticking out of the sides of a smooth metal base. You push it into the socket and twist a quarter-turn to lock it — the same action as a bayonet on a rifle, which is where the name comes from.
E27 (Edison screw) has a spiralling screw thread about 27mm across. You screw it into the socket like a jar lid. The "E" stands for Edison, and E27 is the international standard fitting.
How to tell them apart
The quickest way is to look at the base of your old bulb, or into the empty socket:
| B22 bayonet | E27 screw | |
|---|---|---|
| Connection | Push and twist | Screw in |
| Base | Smooth, two side pins | Spiral thread |
| Size | 22mm across | 27mm across |
| Common in | UK, AU, NZ, India, South Africa… | Worldwide |
Don't force the wrong bulb
Because the connections are different shapes, an E27 bulb will not fit a B22 socket and vice versa. Never force a bulb — you risk damaging the fitting. Adapters that convert between the two are cheap and available, but for a clean, reliable result it is best to simply match your existing fitting.
What about E14, GU10 and MR16?
These are the other common fittings you may meet. E14 is a smaller screw (14mm), used in candle bulbs, lamps and chandeliers. GU10 and MR16 are twist-lock and two-pin spotlights respectively. If you are unsure what you have, our finder can help you identify it.
What to buy
Match your existing fitting exactly. The foolproof method is to take the old bulb with you, or a clear photo of its base, when you shop.
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