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.

NameProduct Code/Stock ReferenceDiameterDiagramImageDescription/Use
Bayonet Cap (BC)B22d22mmB22d DiagramB22d ImageFound in a range of applications, especially domestic
Small Bayonet Cap - double contact (SBC)Ba15d15mmBa15d DiagramBa15d ImageFound in a range of applications, especially domestic
Small Bayonet Cap - single contact (SBC)Ba15s15mmBa15s Diagram Found in automotive/machine applications
Miniature Bayonet Cap (MBC)Ba9s9mmBa9d Diagram 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.

NameProduct Code/Stock ReferenceDiameterDiagramImageDescription/Use
Lilliput Edison Screw (LES)E55mmE5 Diagram Small decorative applications and indicator buttons
Miniature Edison Screw (MES)E1010mmE10 Diagram Often found in industrial applications
Candelabra Edison Screw (CES)E1212mmE12 Diagram An American cap but often used in Europe especially in candle shaped lamps
Small Edison Screw (SES)E1414mmE14 DiagramE14 ImageCommonly found in a range of domestic applications
Edison Screw (ES)E2727mmE27 DiagramE27 ImageThis is the most popular Edison Screw cap and is found in a vast range of applications
Giant Edison Screw (GES)E4040mmE40 Diagram 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 TypeProduct Code/Stock ReferenceDistance between pinsDiagramImage
T4 (13mm)G55mm T4 Diagram
T5 (16mm)G55mmT5 Diagram 
T8 (26mm)G1313mmT8 DiagramT8 Image
T12 (38mm)G1313mm