What does E26 mean?
E stands for Edison screw — a threaded metal base invented by Thomas Edison. 26 is the base diameter in millimeters.
Breaking down the code
| Part of code | Meaning |
|---|---|
| E | Edison screw (IEC and NEMA designation for threaded lamp cap) |
| 26 | Outer diameter of the metal screw base in millimeters |
So E26 = an Edison screw base that is 26mm in diameter. E27 = 27mm. E12 = 12mm. The naming is always the same: letter for base type, number for size.
The full Edison screw family
| Code | Diameter | Common name | Region |
|---|---|---|---|
| E12 | 12 mm | Candelabra | North America |
| E14 | 14 mm | Small Edison Screw | Europe |
| E26 | 26 mm | Medium / Standard | North America |
| E27 | 27 mm | Medium / Standard | Europe, Asia |
| E39 | 39 mm | Mogul | Commercial (NA) |
| E40 | 40 mm | Giant Edison Screw | Commercial (EU) |
Why are there two "medium" sizes?
E26 and E27 evolved separately in North American and European electrical systems, each standardized around different mains voltages (120V vs 240V). They are close enough that most bulbs physically fit either socket, but voltage compatibility still must be verified.
How the G-code pin bases compare
Pin bases use the same logic — G = pin type, number = spacing in mm. GU10 = pin base, 10mm spacing. G4 = pin base, 4mm spacing. The "U" in GU indicates a locking mechanism.