Birmingham Plate Gauge
A separate gauge for sheet metal, because wire rules did not apply.
Origin
Used in the Birmingham metal trades for rolled sheet, particularly brass, gold and silver, from the eighteenth century.
The catch
Wire is drawn through a die and sheet is rolled between cylinders, which are entirely different processes. So the trades that did both needed two gauges, and a number that meant one thickness in wire meant something else in plate.
| Gauge | Inches | Millimetres | Typical use |
|---|---|---|---|
| 1 | 0.300 | 7.62 | Heavy plate |
| 6 | 0.203 | 5.16 | Structural sheet |
| 12 | 0.104 | 2.64 | General fabrication |
| 18 | 0.049 | 1.24 | Light sheet, hollowware |
| 22 | 0.031 | 0.787 | Silversmithing |
| 26 | 0.018 | 0.457 | Fine metalwork |
| 30 | 0.012 | 0.305 | Foil and leaf work |
Birmingham was the centre of the British toy trade, meaning small metal goods rather than playthings: buckles, buttons, snuff boxes, plated ware. Those trades worked in thin rolled sheet and needed finer discrimination at the light end than any wire gauge offered. The plate gauge served silversmiths and goldsmiths in particular, where an error of a thousandth of an inch across a large sheet represented a real amount of precious metal.