There is nothing more confusing to the young
mechanic than the use of the several systems of gauges used in
designating the sizes of wire, machine screws, drills and plate
thickness. Unfortunately, most of these dimensions differ from
each other for corresponding numbers by comparatively small
amounts, yet an amount sufficient to cause error if the one is
mistaken for the other.
The following table gives for comparison values
for only a few numbers under each of the several gauges in most
The dimensions are purely arbitrary. The
American, or Brown & Sharpe gauge, was brought out in the
production of a gauge to overcome the irregularities in spacing
of the Birmingham wire gauge. In this gauge the dimensions
increase by a regular geometrical progression.
The largest dimension is No. 0000, which equals
.46 of an inch. The next smaller number, 000, is obtained by
multiplying .46 by the constant .890522. This product again
multiplied by the same constant, gives the next smaller number,
and in like manner
each number is the product of the preceding number and this
constant. A comparison of the English and American gauges is
best shown in Fig. 225, where the peculiar irregularities of the
former are plainly shown.
The imperial wire gauge differs but little from the English. It
was adopted by the English Board of Trade in 1884 as a
substitute for the Birmingham gauge. The Stubsí steel wire gauge
differs materially from those above cited. Its range carries it
from No. 1 to No. 80, variations in dimensions being indicated
to the nearest one thousandths of an inch. The difference
between consecutive numbers differ in dimensions from one to at
most only a few thousandths, the eighty number carrying it
through but .214 of an inch.
It is extremely unfortunate that a single standard gauge could
not be adopted and used to the exclusion of all others, at least
in our own country, and thereby avoid all confusion incidents to
the promiscuous use of the several so-called standards. Even the
manufacturers of brass and copper stock, who have adopted the
American standard, do not confine themselves exclusively to this
gauge, as much of their product is still gauged by the English
The Stubsí drill gauge varies from the Stubsí steel wire gauge
by from 0 to 3 thousandths of an inch over size, which is simply
the average oversize determined by a great number of
measurements of wire drawn through Stubsí wire gauge dies, and
might be compared with a maximum limit gauge, as the dies, when
worn to such an extent as to produce wire over the sizes
indicated by the drill gauge are replaced by new ones.
It will be noted that as the designating number of gauge
increases the dimensions decrease for all except the steel music
wire and machine screw gauges, which increase in diameter as the
number increases. This also tends much towards confusion, and
may be looked upon as another anomaly of the present gauge
The gauges, or tools for indicating the gauge of wire or plates,
are of two forms, the angular and the notch. The angular gauge
is shown in Fig. 226.
With this tool the measurement is made by passing the screw,
wire or plate into the angular opening until it touches both
sides; the reading opposite the point of contact giving the
gauge of the material. When used for gauging plates, this gauge
should be made with open end, as shown at C. on the one side is
graduated the English and American standards, and on the other
the machine screw gauge and parts of an inch. The notch gauge is
shown in Fig. 227.
In using this tool the article measured should just pass through
one of the slots, the number opposite indicating the gauge.
These gauges may be had with the decimal equivalent of each size
stamped on the back of the tool, which will frequently be found
to be a great convenience.