What Is The Reason For The System Of Gauge Thickness For Sheet Metal?

According to American Institute of mining engineers standard decimal gauge, thickness of the sheet in thousands of an inch show the gauge number. It is very early standard used in 1877. Gauge numbers started from 2. This series consist of 2 to 22 by 2's, 25, 28 to 40 by 4's, 40 to 100 by 5's, 110 to 180 by 15's, and 200, 220, 240, 250 number.

In 1893 US standard gauges were very popular but it is not very useful. Most sheet metal rolled steel did not shaped up the iron and its weight is approximately 502 pounds per square feet. It was very confusing for the manufacturers that either they sold or taxed steel by thickness or by weight per square feet. According to this standard cubic foot shaped iron mass was defined as 480Ib.   

American Railways Masters Mechanics were started using decimal Gauge standard. Decimal Gauge is also known as Master Mechanic gage. Different manufacturer's used different US standard gauge. This standard sold steel by weight not by thickness and is known as Manufacturer's Standard Gauge. For measuring other materials like copper zinc, magnesium and Aluminum completely different gauges are used.