Fig. 1493.
In [Fig. 1493] is shown one of Brown and Sharpe’s notch wire-gauges, the notches being arranged round the edge as shown:
The thickness of a given number of wire-gauge varies according to the system governing the numbering of the gauge, which also varies with the class of metal or wire for which the gauge has been adopted by manufacturers. Thus, in the following table are given the gauge-numbers and their respective sizes in decimal parts of an inch, as determined by Holtzapffel in 1843, and to which sizes the Birmingham wire-gauge is made. The following table gives the numbers and sizes of the Birmingham wire-gauge.
BIRMINGHAM WIRE GAUGE.
| Mark. | Size. | Mark. | Size. | Mark. | Size. | Mark. | Size. |
| 36 | .004 | 26 | .018 | 16 | .065 | 6 | .203 |
| 35 | .005 | 25 | .020 | 15 | .072 | 5 | .220 |
| 34 | .007 | 24 | .022 | 14 | .083 | 4 | .238 |
| 33 | .008 | 23 | .025 | 13 | .095 | 3 | .259 |
| 32 | .009 | 22 | .028 | 12 | .109 | 2 | .284 |
| 31 | .010 | 21 | .032 | 11 | .120 | 1 | .300 |
| 30 | .012 | 20 | .035 | 10 | .134 | 0 | .340 |
| 29 | .013 | 19 | .042 | 9 | .148 | 00 | .380 |
| 28 | .014 | 18 | .049 | 8 | .165 | 000 | .425 |
| 27 | .016 | 17 | .058 | 7 | .180 | 0000 | .454 |
In this gauge it will be observed that the progressive wire gauge numbers do not progress by a regular increment.
This gauge is sometimes termed the Stubs wire-gauge, Mr. Stubs being a manufacturer of instruments whose notches are spaced according to the Birmingham wire-gauge. Since, however, Mr. Stubs has also a wire-gauge of his own, whose numbers and gauge-sizes do not correspond to those of the Birmingham gauge, the two Stubs gauges are sometimes confounded. The second Stubs gauge is employed for a special drawn steel wire, made by that gentleman to very accurate gauge measurement for purposes in which accuracy is of primary importance.
From the wear of the drawing dies in which wire is drawn, it is impracticable, however, to attain absolute correctness of gauge measurement. The dies are made to correct gauge when new, and when they have become worn larger, to a certain extent, they are renewed. As a result the average wire is slightly larger than the designated gauge-number. To determine the amount of this error the Morse Twist-Drill and Machine Company measured the wire used by them during an extended period of time, the result being given in table No. 2, in which the first column gives the gauge-number, the second column gives the thickness of the gauge-number in decimal parts of an inch, and the third column the actual size of the wire in decimal parts of an inch as measured by the above Company.