Gauge
Gauge. The measure of thickness of metal strip and blanks. By custom the thickness of metal is measured by a metal gauge of different calibrations. In Great Britain the thickness of sheet gold, silver and copper is measured by the Birmingham Metal Gauge (B.M.G.). In the United States the Brown and Sharp (B. & S.) gauge is customarily used, it is also called the American Standard (AS). There is also a Birmingham Wire Gauge (B.W.G.), and also several others (including a Jeweler's Gauge). Now just to make things confusing, the instrument to measure metal thickness is called a wire gauge (and it is calibrated in any of those measurements above). When metal strips and blanks are ordered not only is it necessary to spell out the gauge (and which measurement system is used), but also to detail the exact millimeter thickness.
The calibrations are not in even arithmetic increments but in geometric increments, and range from seven-zero (7/0, or 0000000) through one-zero (1/0, or 0), then starting from 1 up (see chart). The higher the number, the thinner the metal. For all practical purposes medals require gauge 5/0 to 8 B. & S. (approximately 1/2 to 1/8-inch). U.S. mints used thickness measurements in inches. Rolls were not gauged to any specific standard. Gauges existed for the thickness of struck coins, but this was largely a matter of ensuring that a pile of coins was the same height from one mint to another.It is almost impossible to observe a struck piece and determine which gauge was used to strike the coin or medal. The amount of relief will distort the estimate, particularly for high relief medals. Multiple striking of medals changes the thickness drastically and also some metal is lost (due to flash when struck with open face dies). Measuring from the high point of one side to the high point of the other side gives the thickness of the struck piece, but this has little bearing on the thickness of the blank from which it was struck. The thickness of coins are measured at the rims (in theory all relief should be below this), medals are indeed measured from high point to high point.In medal striking, an experienced pressman or pressroom foreman must be able to look at a die and determine the gauge of metal best suited for that medal. This is particularly important for medals of precious metal, silver or gold. The pressman is required to use the least amount of material (that is, the thinnest blank) yet still be able to fully strike up the design without causing suction, die draw or breaking a die.A modern trend has been to step down the gauge by one or two numbers; thus a thicker blank will be used making it easier to strike and less likely to break a die. The rising cost of diemaking has required this somewhat unskillful choice of thicker blanks.For collectors there is somewhat of a desire for a thicker blank because of the popularity of a piedfort, a two- or three-, or more thickness blank specially coins or medals created for collectors.For United States For British EmpireB r o w n & S h a r p e Gauge Birmingham Standard WireInches Millimeters Inches Millimeters7/0 .500 12.70.580 14.73 6/0 .464 11.79.5165 13.119 5/0 .432 10.97.46 11.68 4/0 .400 10.16.409 10.388 3/0 .372 9.45.364 9.24 2/0 .348 8.84.324 8.23 1/0 .324 8.23.289 7.338 1 .300 7.62.257 6.527 2 .276 7.01.229 5.808 3 .252 6.40.204 5.18 4 .232 5.89.181 4.59 5 .212 5.38.162 4.11 6 .192 4.88.144 3.66 7 .176 4.47.128 3.24 8 .160 4.06.114 2.89 9 .144 3.66.101 2.565 10 .128 3.25.090 2.28 11 .116 2.95.080 2.03 12 .104 2.64.071 1.79 13 .092 2.34.064 1.625 14 .080 2.03.057 1.447 15 .072 1.83.050 1.27 16 .064 1.63.045 1.14 17 .056 1.42.040 1.016 18 .048 1.22.036 .91 19 .040 1.02.032 .81 20 .036 .91excerpted with permission from
An Encyclopedia of Coin and Medal Technology
For Artists, Makers, Collectors and Curators
COMPILED AND WRITTEN BY D. WAYNE JOHNSON
Roger W. Burdette, Editor