In 1909 the (standardised) round screw-thread was designed for the incandescent lamp that had been patented by Edison. This was combined with a metal final sleeve, forming the so-called Edison Screw. The Edison Screw type is indicated by E (Edison), followed by the diameter of the fitting. E27 is the standard, called Edison Screw - ES abroad. Smaller versions are: E14 (Small Edison Screw – SES), E12 (Candelabra Edison Screw – CES), E10 (Miniature Edison Screw – MES) and E5 (Lilliput Edison Screw – LES). There is only one larger size: E40 (Giant Edison Screw – GES). Therefore, Thomas Edison (the inventor of the light) is also the brain behind the fittings.
The Calex range only includes the E12, E14, E27 and E40 Edison fittings.