Why is the international standard of E26 lamp cap different from the national standard

E26 and E27 are listed as IEC standard specifications. The lighting system of each country varies due to different mains voltage. E26 is mostly used in countries with mains voltage of 100V ~ 120V, and E27 is mostly used in countries with mains voltage of 220V ~ 240V. Therefore, the rated voltage of E26 bulbs on the market is mostly 100V ~ 120V; E27 is mostly 220V ~ 240V and 36V safety bulbs for industrial machines.

The outer diameter dimensions of E26 and E27 threads are relatively close. The difference is that the peak valley depth of e thread is different, and E26 is relatively shallow. In addition, the neck of E27 lamp cap is longer than that of E26, so the two lamp caps should match the lamp holders of their respective specifications. If the E27 lamp cap is rotated to the E26 lamp holder, it will be found that the neck metal will be exposed a lot (easy to cause electric shock). E27 is common in Europe as well as in China. E26 is common in North America and Japan.