Bayonet Caps
Bayonet caps are mainly used in Great Britain and are distinctive by their 'push and twist' action to install. There are many variations of a Bayonet Cap including some three pin versions known as B22d-3 found in new build homes and on some high pressure mercury lamps for industrial use.
Please note measurements are taken across the diameter of the bottom of the cap, not including pins.
| Name | Product Code/Stock Reference | Diameter | Diagram | Image | Description/Use |
|---|---|---|---|---|---|
| Bayonet Cap (BC) | B22d | 22mm |  |
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Found in a range of applications, especially domestic |
| Small Bayonet Cap - double contact (SBC) | Ba15d | 15mm |  |
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Found in a range of applications, especially domestic |
| Small Bayonet Cap - single contact (SBC) | Ba15s | 15mm |  |
Found in automotive/machine applications | |
| Miniature Bayonet Cap (MBC) | Ba9s | 9mm |  |
Found in a range of applications, especially industrial |
Edison Screw Cap
Edison Screw Caps take their name from the inventor of the light bulb Thomas Edison and are universally used for a range of applications. The table below shows the most popular caps but other less common types are available including E11, E17, E26 and E39. It typically follows that the larger the cap the greater wattage and heat the lamp can withstand.
Please note measurements are taken across the diameter of the bottom of the cap.
| Name | Product Code/Stock Reference | Diameter | Diagram | Image | Description/Use |
|---|---|---|---|---|---|
| Lilliput Edison Screw (LES) | E5 | 5mm |  |
Small decorative applications and indicator buttons | |
| Miniature Edison Screw (MES) | E10 | 10mm |  |
Often found in industrial applications | |
| Candelabra Edison Screw (CES) | E12 | 12mm |  |
An American cap but often used in Europe especially in candle shaped lamps | |
| Small Edison Screw (SES) | E14 | 14mm |  |
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Commonly found in a range of domestic applications |
| Edison Screw (ES) | E27 | 27mm |  |
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This is the most popular Edison Screw cap and is found in a vast range of applications |
| Giant Edison Screw (GES) | E40 | 40mm |  |
Commonly used in commercial 250w+ applications |
Tip: It can be difficult to measure exactly the diameter of a cap, especially to the nearest mm, so it is useful to remember that CES fittings are distinctive by their three crests (twists in the fitting), all other Edison Screw fittings have four.
Fluorescent Tubes
Fluorescent tubes typically have two pins at either end but there are exceptions to the rule such as the T12 mono pin. Knowing the pin spacing and wattage of a fluorescent tube is enough to identify the lamp type.
| Fluorescent Tube Type | Product Code/Stock Reference | Distance between pins | Diagram | Image |
|---|---|---|---|---|
| T4 (13mm) | G5 | 5mm |  |
|
| T5 (16mm) | G5 | 5mm |  |
|
| T8 (26mm) | G13 | 13mm |  |
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| T12 (38mm) | G13 | 13mm |
9 Comment(s)
Interesting post about bayonet and Edison screw caps! The details are quite comprehensive. It's amazing how even something as simple as a lightbulb fitting has so much variation. This reminds me of the snake game, maneuvering through a tight space, you've got to navigate all those different cap sizes and types to find the right fit!
It's like a whole secret society of light socket compatibility. The bigger the cap, the greater, it said, interesting! I remember fumbling around trying to fit a bulb in a lamp that took the weirdest size, I had no idea there were so many different kinds, a real Connections Game moment of bulb-fitting frustration.
I once encountered a Level Devil situation when I bought a fancy new lampshade, only to realize my existing bulb had a completely incompatible cap. The struggle was real.
Hey, this is super helpful! I always get a bit lost with all the different lamp fittings. Bayonet caps always feel so solid, unlike those finicky screw-ins sometimes. Thanks for breaking down the sizes and uses so clearly – it's like a cheat sheet for future lighting projects. Even for us Football Bros who just want to see the game clearly, understanding this makes a difference!
I recall a time, attempting to replace a rare vintage bulb for my grandmother's lamp. The new bulb, despite appearing similar, wouldn't fit. After much frustration, I realized the cap was completely different. I desperately needed a Slice Master of cap knowledge then.
Hey there! This is super helpful, especially the detailed breakdown of Bayonet Caps and Edison Screws. I always get those mixed up, trying to figure out which bulb fits where. It's almost as tricky as navigating some levels in geometry dash lite! Knowing about the CES fittings having three crests is a great tip too. Thanks for sharing!
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I remember struggling to find the right lightbulb for a vintage lamp once. It was so confusing with all the different cap types! This guide would have been a lifesaver, especially the clear diagrams and descriptions. It really highlights how important it is to get the details right. If you're ever in a similar bind, checking out a resource like the Cps Test platform could save you a lot of hassle.
Beyond the British Isles, bayonet caps offer a unique twist. My experience with a similar issue involved retrofitting unusual light fixtures in an old theater, a task that felt like navigating a treacherous Slither io game to find the right, obscure bulb for each stage lamp.
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