In fact, the use of "GAUGE" to indicate thickness can be traced back to the beginning of the industrial revolution in the United States. At that time, people who produce wire needed to use a method to quantify the products they sold. Of course, the simplest method was the weight method, but if the buyer only offered to buy 15 pounds of wire, However, if the diameter of the wire is not specified, it will also cause a lot of trouble. Therefore, the wire craftsman will report the diameter according to the number of wire drawing times that they have performed. This is the origin of GAUGE. Since each drawing operation reduces the diameter of the wire, the more the number of drawing times, the smaller the diameter of the wire. Therefore, the larger the number of GAUGE, the smaller the diameter of the corresponding wire.

　　At that time, when steel mills were rolling plates, they found that it was easier to weigh than thickness measurement. Therefore, similar to metal wires, steel plates can be sold using the weight per unit area method. The thinner the thickness of the corresponding steel plate, the smaller the weight per square foot. Therefore, the steel mill believes that the most convenient way to specify the thickness of the steel plate is to establish its own GAUGE number system with reference to the GAUGE number system adopted by the wire-making industry.

　　As for the historical origin of the GAUGE number, it may be determined by the level of productivity development at that time. In the United States in the 18th and 19th centuries, its industrial standards were almost blank. Therefore, each manufacturer had to develop its own standards. With the passage of time and the improvement of the industry level, the standards of these manufacturers have gradually become consistent, and a unified standard wire gauge (SWG) for metal wires, a standard gauge for manufacturers of steel plate materials (MSG) and non-ferrous metals have been gradually established. American Wire Gauge (AWG).

　　Regarding the GAUGE number, a confusing phenomenon is that when you change from one GAUGE number to the next GAUGE number, the amount of change in thickness and weight per unit area is not constant. In fact, if you draw these numbers as a graph, you will see an "exponential decay curve."

　　In other words, the difference between consecutive GAUGE numbers becomes smaller as the GAUGE value increases. For example, the difference between 10Ga. and 11Ga. is 0.0149", while the difference between 35Ga. and 36Ga is only 0.0008". The reason for this difference can be traced back to the origin of the GAUGE number: silk making, which depends on the amount of reduction that can be achieved for each drawing.

　　In order to manufacture thin metal wires, wire-making craftsmen hope to reduce the cross-section as soon as possible. However, due to the limitation of the metallurgical mechanism of material deformation, the amount of diameter reduction in a single pass is limited. Over time, the silk industry has determined the optimal number of passes required for wire drawing. This is also the root cause of the exponential decay curve we see.

　　It needs to be explained that when the non-ferrous metal plate and steel plate have the same Ga. number, the thickness is actually different. For example, 21Ga. corresponds to a standard steel thickness of 0.0329inches (0.84mm); a corresponding galvanized steel thickness is 0.0366inches (0.93mm), and a corresponding aluminum material thickness is 0.028inches (0.71mm).