The spiral lamp holders E27 and E14 refer to the thickness of the lamp holder, that is, the diameter of the lamp holder is different.
E27 is a big screw head (the most common lamp head) we usually say, E14 is the small screw head.
The letter E indicates the spiral lamp holder or lamp cap of the Edison thread, and the number after the "E" indicates the integer value of the outer diameter of the lamp socket, in mm. The outer diameter dimensions of the E27 and E14 bases are 27 mm and 14 mm, respectively. The length of the E27 lamp cap is about 27mm, and the length of the E14 lamp cap is 20-25mm. Simply put, the E27's lamp head heats better, and the E14's lamp head is compact and has a slightly poor heat dissipation.